After checking with V3, V4, V5 & OnStepX (aka V10) everything seems to work well, and I've started a pull request for it to main.

(github's diffs seem broken so especially if looking at the TrackState & similar code, I'd highly suggest just looking at the file instead of diffs.)

The KStars/Ekos Align issue is solved and hopefully any others where a Slew is detected as ending immediately, as I finally found one place that EqNP was set that I missed somehow. (Shouldn't have, but finally.)

kstars/logs$ cat 2021-10-05/* | grep -c "Slew det"
kstars/logs$ cat 2021-10-06/* | grep -c "Slew det"

This is mostly the result of the align module (testing various versions, ~20 for each version tested), the two that happened today were both Meridian Flips triggered by Ekos. This is with 300+ Slews/Gotos in each day's tests. (Full is: "Slew detected, suspend solving...")

I'll let people know when it's accepted, then please try to break it before INDI 1.9.3.

Also OnStepX has the :GX90# fixed in git.