I've been testing timecode sync with my 3 OSMO Action 4 cameras and it seems that there's a timecode bug that causes the timecode to be incorrectly encoded in the file by a drift of 5-6 seconds.  Please let me explain.
Steps to reproduce.
1. Setup your timecode generator for 24 fps.
2. Jam sync your timecode into the camera at 4K/48 fps. Yes, this is not the same but it is a multiple of the timecode generator setup and should work.  This is my broll camera setup for slow motion and thus it must be at a faster frame rate than the other two cameras.  Honestly the bug happens even if you set it to the same framerate.
3. Record your slate/timecode generator so that you can see the time.
4. Power down your camera, pull the battery, wait 30 seconds, put the battery back in, power it up, start recording the slate again for about 30 seconds.

You should now have 2 mp4 files.  Add those to a 24 fps timeline using your NLE (e.g. Davinci Resolve's "Insert Selected Clips to Timeline Using Timecode").  What you'll see is that the second file will insert 5-6 seconds after the timecode that it has recorded in the video.  In other words, the timecode start for the file is 5-6 seconds after the actual true start time of the file.  You can tell this by examining a single frame of video and noting the timecode in the video on the screen of your timecode generator and comparing it to the timecode of your cursor.  They should be the same.

As a former software engineer, this bug can happen if the software captures the start time code of the file 5-6 seconds after the actual recording itself started.  Or it can happen if the code path that captures the start time code doesn't compensate for something that happens only after hitting record after powering on.  For example, quick capture might bypass things to get the recording started quickly and the code that captures the starting timecode isn't taking this into consideration.

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Will this ever get fixed?