I've had this problem lately. On longer sessions Gopro splits the video to multiple files and Racechrono syncs these back together again. So if I make sure the first video file is synced correctly (using GPS data) the following "link after..." video files should be synced too? But they are not. There's a glitch and the sync goes off a second or so.
Here's a short video showing at about ten seconds in what it looks like going from the first to the second video file.

Can this problem be dependent on if I set the Gopro (Hero 7 Black) to HEVC or not?
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I will probably test this over the weekend, but my guess is that this is somehow related to the firmware of the phone, not a general problem on Android, or a problem with the video files generated by your GoPro. I say this because this has been tested a lot in the past and never any problems with it. Also this part of the code hasn't change in maybe 3 years... But this is just a guess, need to do the real world tests.
That said, also new GoPros have a very high bitrate h.265 files, and I cannot say these would have been tested that much...
1) Which Android OS version does your Huawei phone have? Or maybe the Huawei firmware version? I have a few Huawei phones, possibly the P20 with 9.1.xxxx firmware is the closest to yours.
2) Does this happen in analysis too? I wonder if the OS (or the video metadata) is just reporting the video duration wrong?
Yes, running video playback in analysis behaves 100% the same.
I managed to sync the two files correctly instead of just "link after..". I think I GPS-synced the second video and then somehow managed to sync the the first manually. Then the data graph showed the two "video markers" overlapped and only one of them would be visible in the video window. The other one was just black
As the analysis screen behaves the same, the problem is not a video encoding glitch, but a glitch with detecting the video duration. For some reason the video length is detected to be one second longer than reality, causing a blank one second on the exported video (and analysis), the second video going out-of-sync. I will try your videos and see if I can re-produce the problem. If I can, I will probably try a different method of resolving the video duration. Provided that this is a problem with the operating system (or phone firmware), and not the GoPro videos themselves!
Worked perfectly now with 4.6.1 !
Huge thank you!