Extensions can filter requests, alter pages or restrict scripts. A supported private or extension-limited session can help compare browser behaviour, but it does not prove an extension is at fault. Keep normal security protections active.
Use a narrow comparison
Try the same authorised page in a supported browser profile with optional extensions disabled. Record which extensions were active originally. Do not remove password managers or security controls indiscriminately across the computer.
Look for a specific blocked request
A filter may stop an API, script or media resource based on its rules. If one optional extension is responsible, review its documented per-site controls. Only trust a site after evaluating it; do not allow every blocked destination automatically.
Keep other causes open
Browser codec support, CORS and source availability can cause similar symptoms. An unchanged failure in a clean profile points beyond the extension comparison. Report the browser version and exact symptom without exposing a private playlist URL.