Spoke to some of the engineers and they suggest trying File->Utilities->Rebuild to rebuild the indices. Questions are:

1. Does QB hang with a beachball cursor for 40 seconds after making a change? (trying to understand the meaning of "loop" in your description). 

2. What is the OS of the machine doing the sharing?

Still I think using the QuickBooks Server is the best practice - remote mounted drives rely on network file systems that can have issues with locking.