Thanks for the input Matt
I've gone through your list and nothing helps. All those things would make sense if I were doing a jazz arrangement, and I'd do things like that back in the day, but this is the most simple I - IV pop backing.
Check the video I just made of it.
0:09 - plays the C with a #11 despite the key being C, it's playing as though it were G
0:15 - TECHNICALLY if the key is set to C you'd expect the F to not have Bbs, but that's stylistically correct, so all good
0:21 - perfection. Plays the C as a C... but then I have to wonder... why is the program inconsistent with itself?! Every other C is fine, so why is JUST THE FIRST one lydian?!

0:57 - There's absolutely no explaining why BIAB is putting a Db in the bass there. I certainly haven't told it to!
[video:youtube]
https://youtu.be/y0gOfPNp0u0[/video]
There has to be a solution to this. This is day 1, can't get any simpler backings. If it can't handle that, what's the point?