Why were existing videos in Event History converted to HEVC?

Today I encountered the message "This video was recorded using a modern video format called HEVC which is not supported on this browser." It suggested that I switch to Legacy mode, which I did. However, none of the videos recorded overnight can be viewed, only those recorded after I selected Legacy mode. But the REAL issue is that ALL prior videos for this camera in my 60 day Event History now give this message and I am unable to view them. Prior to today I could view all these videos. Therefore, THESE WERE NOT RECORDED IN HEVC FORMAT, but have been converted, after the fact! This is unacceptable in my opinion. Please revert these videos back to the original recorded format.