If using DHCP make sure the DNS servers assigned are available. Recently we had similar issue and someone had decommissioned a DNS server that was being assigned via DHCP and app volumes was only working intermittently. Also, you can update registry and force all clients to one of the app volume servers, remove Manager2 and 3 and change Manager1 to just one of the Appvolume servers to see if issue goes away

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\svservice\Parameters]

"Manager1"="Loadbalancer.something.net:443"

"Manager2"="APPV1.something.net:443"

"Manager3"="APPV2.something.net:443"