Fatal error: Uncaught Error

I recently noticed an error, are there any issues with PHP 7.1? Here is the error that is now showing where the feed was:

Fatal error: Uncaught Error: [] operator not supported for strings in /xxx/wp-content/plugins/feedzy-rss-feeds/includes/abstract/feedzy-rss-feeds-admin-abstract.php:411 Stack trace: #0 /xxx/wp-content/plugins/feedzy-rss-feeds/includes/abstract/feedzy-rss-feeds-admin-abstract.php(694): Feedzy_Rss_Feeds_Admin_Abstract->get_feed_url(Array) #1 /xxx/wp-includes/shortcodes.php(345): Feedzy_Rss_Feeds_Admin_Abstract->feedzy_rss(Array, '', 'feedzy-rss') #2 [internal function]: do_shortcode_tag(Array) #3 /xxx/wp-includes/shortcodes.php(223): preg_replace_callback('/\\[(\\[?)(feedzy...', 'do_shortcode_ta...', '<h3 class="widg...') #4 /xxx/wp-content/plugins/enhanced-text-widget/enhanced-text-widget.php(62): do_shortcode('<h3 class="widg...') #5 /xxx in /xxx/wp-content/plugins/feedzy-rss-feeds/includes/abstract/feedzy-rss-feeds-admin-abstract.php on line 411

Here is my widget code that pulls several feeds from a forum:

<h3 class="widget-title widgettitle">Forum Discussions</h3>
[feedzy-rss feeds="https://www.XXX/index.rss,https://www.XXX/index.rss,https://www.XXX/index.rss,https://www.XXX/index.rss" max="5" feed_title="no" target="_blank" thumb="yes" size="100" default="XXX" summary="yes" summarylength="65" meta="no"]

I have disabled several plugins that are the normal culprits, W3TC, Async Javascript, Autoptimize, etc., no luck.

WordPress Version: 4.7.1
PHP Version:       7.1.0

ACTIVE PLUGINS:
Advanced Database Cleaner: 2.0.0
AJAX Thumbnail Rebuild: 1.12
AMP: 0.4.2
ARVE Advanced Responsive Video Embedder: 8.0.2
ARVE Pro Addon: 3.8.1
Async JavaScript: 1.17.01.22
Autoptimize: 2.1.0
Captcha by BestWebSoft: 4.2.8
Contact Form by BestWebSoft: 4.0.4
Disqus Comment System: 2.86
Easy Social Share Buttons for WordPress 4.1: 4.1
Enable Media Replace: 3.0.5
Enhanced Text Widget: 1.4.5
EWWW Image Optimizer: 3.2.2
Feedzy RSS Feeds Lite: 3.0.5
FooBox HTML & Media Lightbox: 2.3.2.39
Foo Gallery: 1.2.18
Genesis Featured Page Advanced: 1.9.3
Genesis Sandbox Featured Content Widget: 1.1.8
Glue for Yoast SEO & AMP: 0.3.3
Google XML Sitemaps: 4.0.8
iThemes Security: 6.0.0
Meta Slider: 3.4.1
Meta Slider - Pro Addon Pack: 2.6.7
Responsive Lightbox: 1.6.11
Responsive Menu: 3.0.17
Send Images to RSS: 3.2.1
SEO Redirection: 4.1
SG CachePress: 2.3.11
Simple Page Sidebars: 1.2.0
Subtitles: 2.2.1
Use Google Libraries: 1.6.2.1
W3 Total Cache: 0.9.5.2
WP-DBManager: 2.78.1
WP Sitemap Page: 1.6
Yoast SEO: 4.1
Youtube Channel Gallery: 2.4

Any ideas? Thanks.