exported video corrupt on initial part only

With this latest beta I have been re-grading and re-rendering some older videos created with earlier version of Resolve. Specifically they are Mavic 2 PRO Dlog 20-bit source shot 4 years ago, graded into HDR10. Earlier version of Resolve produced good 10-bit HDR output (no corrupt beginnings).

This version for some reason insists on corrupting about 1 second of video in the beginning. I tried to make changes to that part so it would have to work through it, but no difference. However the rest of the video is produced correctly with no issues.

If I re-render some newer videos shot with an Air 2S in HLG (10-bit) graded and rendered into HDR10, no issues. It looks like there is something odd about the older footage shot with the M2P even though the older versions of Resolve did not complain or corrupt.

I am using Resolve Studio 18.5 B3 with NVIDIA as the encoder setting 4K UHD at 10-bit with HDR tag.

Is this a bug?

Some additional research shows a date (approx 4/12/2021) where videos shot after that date produce correctly while videos shot prior to that date have the 1+ second corruption at the beginning. I have two samples one (shot 4/12) that shows the corruption and the other (shot 4/19) that does not. Both are 4K HLG footage shot with the same Mavic 2 Pro. The difference is most likely caused by a DJI firmware change that got installed on my Mavic 2 Pro between those dates. Analyzing the video file with "mediainfo" does not highlight any relevant differences but it might easily be overlooked. It is unclear what exactly did change.

The key here is that V17 variants of Resolve Studio had no issues with either versions of exporting these files in HDR10, but the newer V18 variants do. I don't have enough of the prior versions to re-install in order to find exactly which of the version changes introduced some kind of "pickiness" regarding the source footage.

Further investigation found that if the project starts with any other video but contains the one that created the corruption it works fine. If the video causing the corruption is the first on the timeline, it corrupts the output if not, it works.

I've seen Resolve occasionally go weird when rendering from H.264 to H.264. I find the best solution there is to eliminate the initial H.264 in the equation.

In other words, don't edit with H.264 (or 5). If your camera offers no other recording formats, transcode the original media into something more robust before editing. DNx, Cineform, ProRes.

A quick test might be to do a Render in Place using MXF OP1A DNxHR on that first clip.