I haven't had this happen except once shortly after I joined.
I know another site I'm on will log you out after a week/two weeks even if you're active.
It could just be something in the site, but I don't think it should be happening very often?
It might be best to use the contact us form if it keeps happening, maybe something is going on with your account?
Ah, that's a possibility. But today I have not cleared my history in weeks. Maybe when the Admin tweaks an update on this forum maybe it logs me out? Idk