Spinning wheel occurs sometimes when collapsing File Tree hive

That suggests it may be something system-wide, either in Windows itself or in something that interacts with both Opus and Explorer, such as a shell extension (one which generates icons, perhaps) or antivirus.

If you generate some process snapshots while the freeze is happening, we might be able to use those to tell you what's going on.

Generating some on Explorer.exe may also make sense, as would checking if any other processes are non-responsive or using a lot of CPU/disk/memory when it happens.