Reproduction Steps

1. Enable debug/warning output
2. Embed a video in a lesson
3. View HTML of the wrapper (ie. with class llms-video-wrapper)

Expected Behavior

No warnings/errors shown

Actual Behavior

Depreciated:  mb_convert_encoding(): Handling HTML entities via mbstring is deprecated; use htmlspecialchars, htmlentities, or mb_encode_numericentity/mb_decode_numericentity instead in ...plugins/lifterlms/includes/class-llms-dom-document.php on line 136

This issue has be recreated:

• Locally
• On a staging site
• On a production website
• With only LifterLMS and a default theme