Hanging, frozen, stuck, etc.
Specifically what's happening is the UI thread is locking up - this can happen because the app has truly experienced a fault, or just when it's thinking hard on the main thread. Most operations happen in their own thread without interrupting the UI, but there are a few that still exist.
Ideally, we would not have CAD processing and the UI on the same thread, and there is a long term effort to fix this (and the resulting white UI/black box combo) underway, but that hopefully at least explains why this happens.
Lance Carocci
Fusion QA for UI Framework/Cloud Workflows, and fervent cat enthusiast