Mouse busy over folder tree pane

All of a sudden when I open my standard lister there is a mouse busy pointer when I move the mouse over the folder tree pane.
It takes up to a minute until it is responding again. Some subfolders are also not shown until the busy period is over. I can not remember havin changed anything in my config.
Any idea? Using OPUS 11.3 64bit on win 8.1 update1.

Short update:
The problem seem to exist when I open a shared folder when opening a (standard)-lister (dubble click on desktop)
I changed my standard lister to open a non-shared folder and OPUS is there instantly. I can even open the (originally slow) shared folder immediately afterwards whithout any time delay.
Is this a bug?

I'd suspect an issue with firewall/antivirus, network drivers or possibly the server itself. Opus does the same things regardless of how you open the window and go to the folder, but it might be querying more things at once (or in quick succession) if you open the window starting in the shared folder, which may in turn cause a problem if one of those components can't cope properly.

It's hard to guess, though.

A tool like Process Monitor might show you which operation is taking a long time, which may point to where the problem is.

Also, under Preferences / Folders / Auto-Loading you can set Opus not to go to network folders as soon as you open a window, instead displaying a message you can click on when/if you want the folder to load.