Sharing the problem and the fix...

Upgraded recently from GW 2014 SP2 to GW 2014 R2 HP1. Run the GroupWise client for Windows, go to the mailbox folder, upon right-clicking a message a pop-up menu with options appears, everything seems fine until the mouse cursor hovers over the "Move To" option where GroupWise becomes unresponsive for 10 to 45 seconds (ensued with users with arms up in the air screaming their frustration and you looking bad, after all, you promised better things...)

This happens only with the GW 2014 R2 HP1 client and does not happens if you revert to the GW 2014 SP2 client.

This happens in online or proxy mode, it doesn't happen in cached mode. It doesn't happen with the GroupWise Archives as far as I know.

This happens and seems worse on mailboxes that have a fair bit of stuff in it, i.e. you won't see this happen on a new mailbox.

The only fix for this is a structural rebuild of the mailbox.