Undefined index: priority – checkout page

Am using Storefront child theme with the latest version of Storefront. Since updating to Woocommerce 3.5.1, I find this entry in the debug.log only when on the checkout page.

[03-Nov-2018 18:35:15 UTC] PHP Notice:  Undefined index: priority in C:\server\site\wp-content\plugins\woocommerce\includes\wc-core-functions.php on line 1526

Troubleshooting steps I have taken to try to resolve the issue:

 1. Unset all the billing and shipping fields, still the same entry in the log.

 2. Deactivated all plugins except for Woocommerce, no change.

 3. Deactivated all plugins, except Woocommerce, and activated the Twentysixteen theme, still the same entry is recorded upon going to the checkout page.

I find Woocommerce to be a solid platform and have never had an issue with it, but this one has me baffled.

Below is my System Status report. By the way, the "Table does not exist" didn't happen till I updated to 3.5.0 but everything seems to work fine.

Any help will be greatly appreciated.

### WordPress Environment ###

Home URL: https://localhost.com
Site URL: https://localhost.com
WC Version: 3.5.1
Log Directory Writable: ?
WP Version: 4.9.8
WP Multisite: ?
WP Memory Limit: 256 MB
WP Debug Mode: ?
WP Cron: ?
Language: en_US
External object cache: –

### Server Environment ###

Server Info: Apache/2.4.18 (Win32) OpenSSL/1.0.2e
PHP Version: 5.4.9 - ? WooCommerce will run under this version of PHP
however
it has reached end of life. We recommend using PHP version 7.2 or above for greater performance and security. How to update your PHP version

PHP Post Max Size: 8 MB
PHP Time Limit: 300
PHP Max Input Vars: 1000
cURL Version: 7.27.0
OpenSSL/1.0.2e

SUHOSIN Installed: –
MySQL Version: ? 5.5.48 - We recommend a minimum MySQL version of 5.6. See: WordPress requirements
Max Upload Size: 2 MB
Default Timezone is UTC: ?
fsockopen/cURL: ?
SoapClient: ?
DOMDocument: ?
GZip: ?
Multibyte String: ?
Remote Post: ? wp_remote_post() failed. Contact your hosting provider. cURL error 6: Could not resolve host: www.paypal.com; Host not found
Remote Get: ? wp_remote_get() failed. Contact your hosting provider. cURL error 6: Could not resolve host: woocommerce.com; Host not found

### Database ###

WC Database Version: 3.5.1
WC Database Prefix: 59glf_
Total Database Size: 4.45MB
Database Data Size: 3.45MB
Database Index Size: 1.00MB
59glf_woocommerce_sessions: ? Table does not exist
59glf_woocommerce_api_keys: ? Table does not exist
59glf_woocommerce_attribute_taxonomies: ? Table does not exist
59glf_woocommerce_downloadable_product_permissions: ? Table does not exist
59glf_woocommerce_order_items: ? Table does not exist
59glf_woocommerce_order_itemmeta: Data: 0.06MB + Index: 0.03MB
59glf_woocommerce_tax_rates: ? Table does not exist
59glf_woocommerce_tax_rate_locations: ? Table does not exist
59glf_woocommerce_shipping_zones: ? Table does not exist
59glf_woocommerce_shipping_zone_locations: ? Table does not exist
59glf_woocommerce_shipping_zone_methods: ? Table does not exist
59glf_woocommerce_payment_tokens: ? Table does not exist
59glf_woocommerce_payment_tokenmeta: Data: 0.02MB + Index: 0.03MB
59glf_woocommerce_log: ? Table does not exist
59glf_blogs: Data: 0.02MB + Index: 0.03MB
59glf_blog_versions: Data: 0.02MB + Index: 0.02MB
59glf_commentmeta: Data: 0.02MB + Index: 0.03MB
59glf_comments: Data: 0.02MB + Index: 0.09MB
59glf_links: Data: 0.02MB + Index: 0.02MB
59glf_options: Data: 2.30MB + Index: 0.06MB
59glf_postmeta: Data: 0.47MB + Index: 0.31MB
59glf_posts: Data: 0.17MB + Index: 0.06MB
59glf_registration_log: Data: 0.02MB + Index: 0.02MB
59glf_signups: Data: 0.02MB + Index: 0.06MB
59glf_site: Data: 0.02MB + Index: 0.02MB
59glf_sitemeta: Data: 0.11MB + Index: 0.03MB
59glf_termmeta: Data: 0.02MB + Index: 0.03MB
59glf_terms: Data: 0.02MB + Index: 0.03MB
59glf_term_relationships: Data: 0.02MB + Index: 0.02MB
59glf_term_taxonomy: Data: 0.02MB + Index: 0.03MB
59glf_usermeta: Data: 0.06MB + Index: 0.03MB
59glf_users: Data: 0.02MB + Index: 0.05MB

### Post Type Counts ###

attachment: 97
cfmemailverification: 1
displayed_gallery: 2
faq: 13
fmemailverification: 1
form-entries: 2
form-maker_fmc: 1
kbs_form: 1
kbs_form_field: 5
kbs_log: 2
kbs_ticket: 1
ksd_reply: 1
ksd_ticket_activity: 1
nav_menu_item: 53
page: 23
popup: 4
popup_theme: 6
post: 1
product: 24
product_variation: 40
shop_order: 3
stgh_ticket: 4
stgh_ticket_comments: 4
ufaq: 1
vtmin-rule: 1
wcccf: 3
wccpf: 13
woo_faq: 3
wp_email_images: 1
wpforms: 1
wysijap: 1
ywcm_message: 1

### Security ###

Secure connection (HTTPS): ?
					Your store is not using HTTPS. Learn more about HTTPS and SSL Certificates.
Hide errors from visitors: ?

### Active Plugins (33) ###

Arconix FAQ: by Tyche Softwares – 1.8.3
Autoptimize: by Frank Goossens (futtta) – 2.4.1
Cache Enabler: by KeyCDN – 1.3.1
CDN Enabler: by KeyCDN – 1.0.8
Classic Editor: by WordPress Contributors – 0.5
Custom Product Tabs for WooCommerce: by YIKES
Inc. – 1.6.6

Frontend Uploader: by Rinat Khaziev
Daniel Bachhuber – 1.3.1

Heartbeat Control: by Jeff Matson – 1.2.5
Homepage Control: by WooThemes – 2.0.3
Nav Menu Roles: by Kathy Darling – 1.9.2
Plugin Organizer: by Jeff Sterup – 9.5.1
Purchased Items Column WooCommerce: by pipdig – 1.2 – Not tested with the active version of WooCommerce
Remove jQuery Migrate: by Hendy Tarnando – 1.0.1
Responsive Lightbox & Gallery: by dFactory – 2.0.5
SI Captcha Anti-Spam: by Mike Challis – 3.0.4 – Not tested with the active version of WooCommerce
Storefront Hamburger Menu: by WooCommerce – 1.2.2
Storefront Top Bar: by Wooassist – 1.1.1
Tutsplus display WooCommerce products and categories/subcategories separately in archive pages: by Gary Finley – 1.0 – Not tested with the active version of WooCommerce
WC Custom Thank You: by Nicola Mustone – 1.2.1 – Not tested with the active version of WooCommerce
WC Fields Factory: by Saravana Kumar K – 2.0.7 – Not tested with the active version of WooCommerce
WC Variations Radio Buttons: by 8manos – 2.0.2
WooCommerce: by Automattic – 3.5.1
WooCommerce Admin Bar Addition: by David Decker - DECKERWEB – 2.7.0 – Not tested with the active version of WooCommerce
WooCommerce Cart Tab: by jameskoster – 1.1.2 – Not tested with the active version of WooCommerce
WooCommerce Email Validation: by Hugh Lashbrooke – 2.1 – Not tested with the active version of WooCommerce
WooCommerce Money Order Gateway: by Gary Finley – 1.0 – Not tested with the active version of WooCommerce
WooCommerce PDF Invoices & Packing Slips: by Ewout Fernhout – 2.2.4
WooCommerce Product SKU Generator: by SkyVerge – 2.3.4 – Not tested with the active version of WooCommerce
WooCommerce Sequential Order Numbers: by SkyVerge – 1.8.3 – Not tested with the active version of WooCommerce
WooCommerce Show Attributes: by Isabel Castillo – 1.6.4 – Not tested with the active version of WooCommerce
Woocommerce Table Rate Shipping: by JEM Plugins – 2.0.0 – Not tested with the active version of WooCommerce
WP Retina 2x: by Jordy Meow – 5.4.3
WWM Social Share: by Jobin Jose – 2.1

### Settings ###

API Enabled: ?
Force SSL: –
Currency: USD ($)
Currency Position: left
Thousand Separator: ,
Decimal Separator: .
Number of Decimals: 2
Taxonomies: Product Types: external (external)
grouped (grouped)
simple (simple)
variable (variable)

Taxonomies: Product Visibility: exclude-from-catalog (exclude-from-catalog)
exclude-from-search (exclude-from-search)
featured (featured)
outofstock (outofstock)
rated-1 (rated-1)
rated-2 (rated-2)
rated-3 (rated-3)
rated-4 (rated-4)
rated-5 (rated-5)

### WC Pages ###

Shop base: #122 - /shop/
Cart: #5 - /cart/
Checkout: #6 - /checkout/
My account: #7 - /my-account/
Terms and conditions: #1005 - /terms/

### Theme ###

Name: Storefront Child
Version: 1.0.1455305977
Author URL: 
Child Theme: ?
Parent Theme Name: Storefront
Parent Theme Version: 2.3.5
Parent Theme Author URL: https://woocommerce.com/
WooCommerce Support: ?

### Templates ###

Overrides: storefront-child/woocommerce/archive-product.php
storefront-child/woocommerce/cart\cart-empty.php
storefront-child/woocommerce/cart\cart.php
storefront-child/woocommerce/cart\proceed-to-checkout-button.php
storefront-child/woocommerce/checkout\terms.php
storefront-child/woocommerce/emails\customer-new-account.php
storefront-child/woocommerce/emails\plain\customer-new-account.php
storefront-child/woocommerce/global\form-login.php
storefront-child/woocommerce/global\quantity-input.php
storefront-child/woocommerce/myaccount\dashboard.php
storefront-child/woocommerce/myaccount\form-login.php
storefront-child/woocommerce/order\order-details-customer.php
storefront-child/woocommerce/single-product\add-to-cart\simple.php
storefront-child/woocommerce/single-product\add-to-cart\variation-add-to-cart-button.php
storefront-child/woocommerce/single-product\product-image.php
storefront-child/woocommerce/single-product\rating.php
storefront-child/woocommerce/single-product\tabs\tabs.php