Im not in private mode. So far it hasnt disconected.
Are you maybe logging in from a different browser/computer/device sometimes?
Does your IP change?
I browse the forum from two IPs, and I don't get logged out when switching IPs, so in my experiencie this isn't relevant.
Changing device does. When I log in from my computer, from a different IP, my phone will always get disconnected. Or logging out from one of the device, I can't remember which.