Can't unload any world paritions

When I open my level that uses world parition, normally it used to open empty - with no partitions loaded.
Now it opens loading all partitions and I can’t unload them:
partitions

I tried loading some smaller section, closing the editor, reopening.
I tried selecting everything loading region from selection, then unloading - nothing.
I removed binaries and intermediate folders and retried the above - still no go.

What might be the cause?