My site goes to maintenance mode spontaneously almost every day. I am advised by users.
Everything works fine when I put it out of maintenance mode.
Any explanation is welcome
This can have a lot of reasons but I try to help to investigate:
maintenance_mode. Based on the results you should have a clear view which code parts may change it's state.
If you're having both live and staging instances, and using caching (memcache for example) check your caching configuration.
If your staging configuration is (by error) set to the same key it may be interfering with the live site, where the live site is reading the configuration from cached staging data, or something of the sorts...