swag72:
The Mesu 200 should be keeping the guide star within a few pixels during a 10 minute period even with no guiding active. If it is not doing that, then there are only a few things to check: Is the mount set to Sidereal Rate, as opposed to lunar, solar, custom, etc? Poor polar alignment. You said your polar alignment is within a few arc seconds. With all due respect, that seems unlikely to me. Even getting polar alignment to one arc minute is a challenge. Finally, periodic error correction. If PEC is not enabled, it is possible that periodic error might move the star that far off in 10 minutes.
As reference data -- my AP1100GTO is permanently mounted; its polar alignment is about 1.5 arc minutes (according to PHD2); I am imaging at 2500mm. I have PHD2 paused during auto focusing. The auto focusing routine runs about 3 minutes. During that 3 minutes, the guide star (OAG) drifts about 4 arc seconds. PHD2 easily pulls the guide star back to center when the auto focus routine is done.
Charlie