WYSIWYG editor broken. After WordPress update?

Hi

[See end for support info]

Customizr seems to have an issue with the current WP version that maifests as a broken wysiwyg editor on any custom fields (ACF) that require it when creating a new post.
The issue goes away if I use any other theme.
I have tried dropping back to the previous version of Customizr (I’m sure I allowed an update on it last week) but the issue persists.

At about the same time I allowed the update to the latest version of WP.
(Did not have this issue prior to last week)

This is a huge issue for me as the site relies on the layout Customizr allows, and at the moment the only way I can create new posts is to swap themes, post, then swap back.
Luckily the site isn’t live yet, but I was hoping to make it so this week.

The error information given in the console is:

post-new.php:3305 Uncaught TypeError: Cannot read property 'addStyle' of undefined

(anonymous function)	@	post-new.php:3305
i	@	wp-tinymce.php?c=1&ver=4401-20160726:9
fire	@	wp-tinymce.php?c=1&ver=4401-20160726:9
initContentBody	@	wp-tinymce.php?c=1&ver=4401-20160726:12
init	@	wp-tinymce.php?c=1&ver=4401-20160726:12
(anonymous function)	@	wp-tinymce.php?c=1&ver=4401-20160726:12
(anonymous function)	@	wp-tinymce.php?c=1&ver=4401-20160726:5
n	@	wp-tinymce.php?c=1&ver=4401-20160726:4
p	@	wp-tinymce.php?c=1&ver=4401-20160726:5
loadScripts	@	wp-tinymce.php?c=1&ver=4401-20160726:5
loadQueue	@	wp-tinymce.php?c=1&ver=4401-20160726:5
t	@	wp-tinymce.php?c=1&ver=4401-20160726:12
render	@	wp-tinymce.php?c=1&ver=4401-20160726:12
execCommand	@	wp-tinymce.php?c=1&ver=4401-20160726:13
init	@	input.min.js?ver=4.4.8:2
(anonymous function)	@	input.min.js?ver=4.4.8:2
each	@	load-scripts.php?c=1&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-mo…:2
each	@	load-scripts.php?c=1&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-mo…:2
(anonymous function)	@	input.min.js?ver=4.4.8:2

I have seen someone else reporting this issue. Do you have any idea of the cause yet please?
(Please don't just 'referred to developers' this one)

Many thanks,
Paulio

<strong>Required setup info:</strong>
# SITE_URL:                 https://intranet2.tiaa.co.uk
# HOME_URL:                 https://intranet2.tiaa.co.uk
# IS MULTISITE :            No

# THEME | VERSION :         customizr | v3.4.21# WP VERSION :              4.6
# PERMALINK STRUCTURE :     /%postname%/

# ACTIVE PLUGINS :
Active Directory Integration: 1.1.8
Advanced Custom Fields: 4.4.8
Advanced Custom Fields: Categories: 2.0.0.8
All-in-One Event Calendar by Time.ly: 2.5.10
bbPress: 2.5.10
Bookly Lite: 7.6.1
BuddyPress: 2.6.2
Collapsing category list: 0.4.1
Custom Menu Wizard: 3.3.0
Display Widgets: 2.05
Invite Anyone: 1.3.11
Posts Table Pro: 1.2.1
Restrict Author Posting: 2.1.4
SiteOrigin Widgets Bundle: 1.6.5
Wp Mail Bank: 1.45

PHP Version:              5.6.19
MySQL Version:            5.6.29
Web Server Info:          Apache

WordPress Memory Limit:   40MB
PHP Safe Mode:            No
PHP Memory Limit:         256M
PHP Upload Max Size:      40M
PHP Post Max Size:        40M
PHP Upload Max Filesize:  40M
PHP Time Limit:           120
PHP Max Input Vars:       1000
PHP Arg Separator:        &
PHP Allow URL File Open:  Yes
WP_DEBUG:                 Disabled

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