Managed servers are plain ones with custom deployments OR were those configured using any of Oracle standard products e.g. FMW components like SOA, WCC?
Also, in such situation, did you try to check the server state using WLST?
Check if you Managed Server was configured to restart automatically when a stuck thread was detected.
Login wls->Environment->Servers-><Manage Server Name>->Monitoring->health
check "restart with stuck thread".