Thanks Jerryyy!
I never worked out how the AE-L and AF-L buttons worked ! I didn't realize they are only(?) active when selecting MF... I thought MF was (as with Nikon) a disconnect of the AF-motor between the body and the lens.
Now I get it, wow, huge improvement !
Thanks Jerryy. Good to hear you've had no problems. The 150-600mm looks amazing. I'm now flipping a coin on whether to jump up to the x-t4 and get one less lens in the short term. Thinking the body might be a better long-term prospect. I appreciate your thoughts. Andrew