This has recently become a problem for me too. We have a few 2055dn's and at least one has started to show these symptoms. Within less than 5 minutes of being powered on it will go offline and stop responding until restarted. I have updated the firmware on our 2055dn that is having problems from v.37.10.sd to v.37.12.ir6508 and saw no change in the symptoms.
I have tried some of the other mentioned fixes as well: shortening the timeout period, disabling SNMP, disabling IPV6. None of this seemed to fix the issue either.
I would like to try this new firmware as well. I'll try anything that may fix this!