Bad stars and problems focussing

I can't help you with auto-focusing because I don't use it. The image you posted looks like a small part of your frame, maybe from a corner? Seeing the full frame would be helpful. Maybe manually focused to help sort things out?

You have a significant amount of tilt, might be in the objective glass but I can't really be sure. Remove the FF and test again at the center of frame. No auto-focuser. I downgraded the same scope to guider as it wasn't worth for much else…

A high degree of tilt makes focusing difficult, in a way similar to what defocusing does but probably not as extreme. I am no expert in how auto-focusing work as I don't use it but my guess is that it would be fair to assume this to be at least a contributing factor. As said before, the best way to assess this to remove everything but camera and scope and test again.

I'm seeing this on most nights. Although the seeing hasn't;t been great recently, my other scope is focusing perfectly every time, even when pointed at roughy the same area of the sky.

According to ASTAP, there is also no tilt in the system

You do know that it's not a requirement to use auto-focus to get things in focus right. In your post you state that the stars are not right, even when in focus. You should be able to set up a 1 or 2 sec. exposure loops and manually focus. Zoom in to some medium bright stars ear the center of the frame and make then as small as you can. You can also monitor your FHWM or HFR and tweak it to get the number as small as possible. With a little practice you should be able to get into the critical focus zone. We know you don't have tilt so if your stars still look like comets then you'll know, it's a problem with the optics.