All drone footage become choppy & frozen frames in Premiere?

I've been filming and editing with the same drone and the same computer for a while with no issue whatsoever, however last week following some YouTube video... I changed the export setting from H.264 to H.265, then all my drone clips became choppy frozen frame (on an iMac with M1 chip).

From this point on, all my drone footage's like this whenever I drag them onto the timeline. It all plays perfectly on the source monitor, but when you play it in the program monitor from the timeline it basically becomes powerpoint... Changed export settings back to H.264 long ago, restarted Premiere and tried different footage from different drive, just couldn't even view the footage normally. Is this because the first time I export in H.265 it changes some setting on the back-end or media encoder? Anyone knows how to revert this back to before I changed the export setting?