There's a couple possibilities to what causes a logout:
- Cookie loss. Can you check your cookies that are sent to the server when you get logged out?
- IIS App Pool Restart. Check Event logs, is your site recycling frequently?
- Web Farm/azure. If you are running on a web farm, or azure, it may be switching you to different servers in which case you should look at the devnet article on storing session either in sql (better), or best use azure Redis cache (best)
- Perhaps there is a bug and you need to hotfix, what version of 10 and is there anything already fixed in the Download hotfix bug listing on here?
Can you check those and report back?