+1
Yikes, this is a tricky one. I spent a few hours trying to figure out wtf was going on and still couldn’t pin down the cause. After finding this post I can confirm I’m experiencing the same issue. I’m using UE 4.26 installed from the launcher.
I guess for now I’m going to remove the retainer box, which seems to fix it, but is undesirable because I think it will result in a considerable performance hit.