Artifacts in iMovie

Hello all,

I have macbook pro 2017 base model with the latest Catalina MacOS and latest iMovie. I have created iMovie project on my iPhone 11 pro with latest osX and all the clips were recorded with this phone.

I wanted to finish my project on Macbook pro, so I airdroped project from phone to the macbook.

Now during editing in iMovie I can see some ugly artifacts during crossfade transition (or just after transition) from one shot to another one. This artifacts are visible in iMovie and also in exported video. Strange thing is, that after few plays of the shot in iMovie, artifacts disappeared. However, then they again appear after some time.

I've tried to delete transition and also shot and import it once again, however artifacts appeared again. I am not able to export video without visible artifacts. I can also see that in some artifacts I can see shot from another part of the project, upside down.

It's very strange, don't know if it is related to fact that project was airdropped from iphone or not. On the iPhone I can't see any artifact. I didn't do any video on the macbook directly so can't tell what's wrong, where is the issue, but for sure somewhere is pretty ugly bug - looks like graphic driver doesn't work properly. The strangest thing is that after few play of the part of the project, artifacts disappear for some time.