Recent problem with exported video

[Любовь0101]

Good evening!

Could you please give me some advice? The problem with exported video appeared a month ago. After exporting the project into format H.264 I noticed that video contained flickering frames with square pixels. You can see the result here:

https://youtu.be/VmGWjMsmdY4?t=429

I used default settings except the video format and GPU-acceleration:

It would be great if you could help me to fix this trouble. 

[basil1891]

1) Does the issue appears in the exported file before uploading to YOUTUBE?
2 ) Have you compared Software and GPU-accelerated exports, any difference?

[basil1891]

just in case reminder, don't export all sequence, 2-4 min with a problem part would do