there is also a bug in Quicktime>conversion with frame rates. Never leave the setting on current. Set the actual frame rate or it sets incorrect metadata in the quicktime file. I have had editors send me Qt conversion files for sound post in Fairlight and it always shows the wrong frame rate.
Fairlight, like QT player, is getting the info from the metadata which is incorrect and may make QT player behave badly on playback and certainly incorrectly flag the actual frame rate.
Best, as David has said, is to avoid Qt Conversion and use Compressor for H264 files