Hello @bengmusic ,
It seems that in UE 5.7 this issue is related to a change in the implementation of the blur system. In one thread, a very similar error is mentioned to the one you’re experiencing, although in that case the main problem was a crash.
They suggest trying a console command as a possible workaround(although it’s still a workaround), which in some cases could helps restore the blur’s correct behavior. This way, you might not need to set Corner Radius = 0 and lose the rounded corners.
Additionally, it’s mentioned that an official ticket has already been opened with Epic and that the team is aware of the issue, so it will likely be fixed in a future engine update.
Hope it helps!