You are forced to restart Enterprise Vault (EV) services periodically in order to make the server operational after receiving event ID 41050 for the Lotus Domino Mailbox Archiving Task.
Event ID : 41050 Unable to initialize Names and Address Book (NAB) session for Domino server: 'Failed to create Notes Session (mutex)
Event ID 41050 can have various root causes that are currently being investigated. It is recommended to contact Enterprise Vault Support and open a support case so that each instance can be fully investigated to determine root cause and the appropriate resolution.
This issue has been addressed as part of the following release:
Enterprise Vault 9.0.4 - Release Details