Here is the problem . . .
Right panel Ha obtained May 14. Properly centred.
Left panel R on the 16th-17th. Off-centre.
Same reference frame used both nights. I tried both ASTAP and PS2 and got the same off-centre result on the LHS panel.
I think, but am not positive that v. 126.96.36.1998 was used on the 14th and v.188.8.131.529 on the 16-17th.
No other changes.
I have never seen this behaviour before.
Presently still imaging and not able to provide the log file link.