Hanging WUs in VINA is a known issue that has been around since WCG projects started using VINA many years ago. It's not uncommon but not pervasive enough for the staff to dedicate time to fixing it. It seems as though a WU gets into a calculation loop due to a timing issue of some sort. I just stop and restart BOINC, the WU will reload from a checkpoint, then complete as a valid WU. There was also the known issue of the WUs hanging on completion on Android devices. Those would get close 100% and stay there for hours for some reason. IIRC, they did eventually finish and were valid