I'm always out there somewhere.. It just depends on where I am 
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We did have these issues from time to time as well. It seems that when a lot of computers do a startup all at once Appvolumes agent cannot connect them correctly, this could be due to a lot of things, not just the Appvolumes manager. During startup Appvolumes agent connects to the manager as well to check and see if there are appstacks assigned to the machine account. We saw the same thing happening in the log files. Computer could not connect to manager so when a user logs in appstack attachment failes. Only option is to log off and on again I'm afraid
In regards to why this is happening. Do you happen to have more than 1 Appvolumes server? If not, I would suggest load balancing the managers. Also make sure that you have enough threads to process the bootstorm. 120 users is not that much to be honest.
Other 2 more heavy options are to restart the Appvolumes servers at night (make sure to have more than 1 manager and do not reboot at the same time) or to have some sort of PS script that checks the svservice.log file on this error and restart the machine if his error does show up.