Just the same problem. This seems to be because in CKEditor 4.1 they added an additional content filter. And in fact, if the plugin does not explicitly say that some tags like <video></video> allowed, they will simply be deleted by the source editor !!! My workaround was to disable ACF in the editor by adding the following line at the beginning of the ckeditor / config.js file:
CKEDITOR.config.allowedContent = true;
Thus, the source code editor no longer checks the contents of html, so it accepts everything! As a result, the <video>...</video> no longer deleted!
Interception helps
Greetings -Christian
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