I have a Problem with v.1.2.9 which seems to throw the boarding logic off quite a bit,
whenever i go EVA and re-enter a Vessel I have a "duplicate" of that Kerbal blocking the exit from then on.

With v.1.2.3 this bug seems to be gone though.

Game Version 1.1.2(1260)

Is anything from the list applies to you: https://github.com/KospY/KIS/wiki/Known-incompatible-mods?

Hi again, sorry for the late reply.
Found out that Kerbal Krash System got installed with Kerbalism in my CKAN, removing KKS seems to have fixed the issue, along with reinstalling the latest KIS version.
Kerbalism seems to work so far with KIS so you might want to check the compatibility for it again.

Anyway thank for helping me solve this problem!