Concerning the focuser motion, believe me, up to now I built three of those things and tested them extensively. I've never seen anything strange happen after a series of forward and backward movements, like the ones you suggest, by issuing direct "go to" commands.
Indeed other focus algorithm in Ekos do work, such us polynomial and linear. It's just the one pass linear which gives this weird results... it must be something really stupid but devilish.

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