You are probably experiencing the known issue of lots of files being opened up in the Attach folder?

I was able to fix it on the problem workstations by running QB update and force the reset.

Make sure all updates get run, restart and check to makes sure all the updates are current.

And then I use Control Panel to repair QB, restart and I can get the problem workstations running.

You might want to also do an update reset on the server, restart and then run the control Panel repair.

I've been supporting QB for decades and I HAVE NEVER had the QB HUB Tool DO ANTYHING for me! NEVER!