The focus on my CPC 1100 HD changes after goto slews much to my amazement.
As far as I know that is usually due to mirror flop of the primary mirror on the primary's outer baffle tube carrier? It sounds like the primary mirror is slightly loose, like when e.g. on Meade SCT's / Mak's, the section to the rear of the mirror that the focusser arm screws into which screws on, is not screwed on quite tight enough, and there is a slight space between it and the large O ring and then the primary mirror and then the cork ring around the front of the primary and the metal ring at the front holding it onto the outer baffle tube. So the mirror can flop from left to right, as it were, in the tube as the tube goes to different orientations, and collimation / focus can shift as a result.
I can show you the idea of the mechanism in these pictures from when I took my Meade 7" Mak apart to remove the internal 3.5 Kg weight ;- https://plus.google....976030517144...
Fortunately when I checked my 7" Meade's Mak's 8 1/4" primary it was firmly held and would not rotate or flop even slightly.
I think Celestron RTV glues their primaries onto the carrier though, where Meade does not, which may present you with problems?
If your primary flopping around slightly is the cause, you will need to have it repaired by Celestron if under warranty, or take the corrector off (noting the corrector position exactly), pull the metal C clip off the inner baffle tube, pull the primary out by the outer baffle tube, and tighten the assembly. Be careful not to rotate the primary or to tighten too much which could cause Astigmatism. The part at the back of the primary which the focusser arm screws into is held on to the end of the outer baffle tube by a screw thread and a couple of grub screws it seems. Make sure not to tighten them too much or you will crush the threads. Needs only just sufficient to hold it firmly with no movement.
I've seen this happen before on the forum, and that was the solution to the problem. If the mirror flops a lot, collimation will be affected and your planetary views at high power will be affected badly I would assume.