I have been dealing with this weird thing with Rush. I am on an iPhone 11 and shoot 4K. When I take the videos, they're fine. However, when I put them into Rush, a couple parts of a few videos will become pixilated for a split second. Never longer than 2 seconds or so, but it's enough to render the clip useless. I don't know how to fix it, what I'm doing wrong to cause this, and it's ultra frustrating. Sometimes it will freeze, and I can't do anything besides exit the app. Other times it will open but the audio won't play, nothings muted and my device audio is up. Plus, today the app just crashes mid-edit and all my work is gone. I don't know how an app from Adobe can be stood by--by Adobe--with these blatant and annoying flaws. I am a paid subscriber too which is all the more frustrating.
Sorry for the frustration. Do you have any effects added to the project? Could you try signing out and back into Creative Cloud and see if that helps? Does your project are synced to Creative Cloud? https://helpx.adobe.com/in/premiere-rush/help/project-syncing-premiere-rush.html#:~:text=Sync%20stat....
.Let us know.