Hello, the bug is present on the latest version of Chrome(72.0.3626.81) and Edge(42.17134.1.0), but not on Firefox and IE11. Yes I did try to remove every other plugins and use the latest default WP Theme (TwentyNineteen), same behavior. The bug is only present on a WYSIWYG inside an ACF field group in a page. Using the classic editor in a Gutenberg block works, and installing the “Classic Editor” plugin removes the issue entirely.
Here is a video showing everything I just said:
https://photos.app.goo.gl/ZFMU7y9qbHtSzqWV7
