RMS Crashes During Purchase Order

I had made a post about this before but never found a solution to it, so I'm reposting it.
One of our clients have been having some issues with purchase orders. They have two lanes running the newest version of RMS, one of which is the server.
First when adding items to a purchase order, if any item is rung up in the other lane it is added to the purchase order. This is a reproduceable result.
Secondly, sometimes when adding items to a purchase order, if they change focus away from that window, all the items will be removed. Note that they aren't closing the window, merely switching to another open application or window inside of Store Ops Manager. I have not been able to see this reproduced but they assure me that it happens often, and that it happened 4 times on one specific purchase order.
Third, they randomly get the error message "Error 3711: Operation cannot be performed while executing asynchronously" when doing purchase orders which causes them to lose the PO.
I had tried a few things, nothing too major, and I thought it was better but they had just neglected to call me to tell me the problem was continuing.
Any help would be appreciated.

Any ideas? Specifically the part about the message "Error 3711: Operation cannot be performed while executing asynchronously" is the most important. I think I have fixed the other errors with hotfixes and program updates.