Robin
both with ext4 formats.
Consider this possibly a symptom of lazy init on single core machines. (Have observed similar issues on different syncing tasks, other than installing, myself already) Then the postponed initialisation causes trouble and mimics a stalled execution, while simply this init stuff takes up all available resources. So you might want to try to make sure the lazy init of the freshly created ext4 drives was completed before proceeding with writing/installing something on and syncing to them. Depending on drive sizes this process can take up to some hours.
I found the statement from the kernel log, that this lazy thing won’t interfere with any normal operation, to be only true on multicore machines.
Windows is like a submarine. Open a window and serious problems will start.