Errors when bot supplies its own session ID?

Do you have sess_match_ip enabled? If you do, and if the bot switches IP addresses while crawling ... that's most likely the problem.

CI does take this into account, but your database table needs to be properly setup as well. The DB error suggests that it only has the "id" column as the primary key, while it needs to be a composite of id, ip_address if you've enabled match_ip.

Dang it. I am guilty. Nows when you scold me about reading the user guide.

I'd be annoyed if you reported it as a bug via GitHub, but not here really ... not for this. It's an easy mistake to make and one that I anticipated.