No video thumbnails sometimes in bridge

[mastix]

When I try to browse video files (ProRes transcoded with Kyno from DNxHR) sometimes thumbnails are created and sometimes not. Same kind of files some have thumbnails and some not (only the icon of the program I use to view video files (SM player) It is confusing me as sometimes opening a folder created the thumbnails quickly but when I jump to the next folder those are not created although I can play them but with no thumbnail Bridge is of no use to me. Why is this randomly happening?

[mastix]

Ok Just saw that if I purge the cache with right click on the mouse sometimes video thumbnails get generated and sometimes not (for example h265 from the mavic 2 pro do not get generated even with purge cache option.