Neil , I dont see anything wrong with your set up , it's almost identical to what I have on my C9.25 and I don't have any problems and focus is found easily in all my eyepieces , mainly TV's Plossl's , Radians , Panoptics and Naglers all reach focus .
I would put my money on the mirror lock not fully releasing fully .
Can you see the primary moving when the focuser is turned both from the front of the OTA and looking it the diagonal without an eyepiece as you should see it moving back and forth .
Here is mine , as I said almost the same as yours .
Good luck .
Brian.