Invalid Servo Chain, despite being valid

[Delliardo]

Craft file and KSP.log

https://web.tresorit.com/l/vSn4u#hHDK6nw9OV-bEwXskwKBnw

https://i.imgur.com/mFSFxAr.png

After grappling the PMA on the unity assembly, undock the bottom docking port from the shuttle. For some reason the control changes from the shuttle cockpit to something else (I haven't narrowed down which part becomes the control). You'll have to switch control back to the shuttle cockpit. Then when you try to make the top docking port on the unity assembly the effector, Easy Robotics says no.

[Delliardo]

Update: So I noticed that any docking node (Grapple fixtures, CBM Active type II, And the androgynous docking port) that wasn't attached to something and then undocked would have the issue. However I tried putting a cap on the docking port I want to use, then undocked the cap, but it still counts as an invalid servo chain when selected as an effector.