I had him as a companion and then initiated the Castle quest. He left me to go gather troops outside the Castle. I met him there and completed the quest, and I am pretty sure at that point he wouldn't follow me, but I chalked this up to the fact that I hadn't gotten the radio tower going yet. So I fast traveled to Sanctuary, got the materials I needed, went back to Castle and got the Radio Antenna working, and he congratulated me, and then just like walked away, I couldn't initiate a normal companion/settler interaction, I could stop him and he would say whats up but thats it.
Eventually I found him again in Sunshine Co-op, where he had been stationed before I made him my companion, and same thing he is not intractable. I have tried killing him and dismissing my other companions and lots of other stuff. Have read that several other people are experiencing this issue. Please fix.