Well, I did some more testing and I loaded up a save BEFORE I went into the Endless Paths. I was able to enter into Bright Hollow and zone to the second floor AND I was able to switch party members.
My suspicion is that its based on his personal quest.
Until I am assured this is fixed...I think I am just going to skip recruiting him entirely on subsequent playthroughs.
Okay. I did some more testing and I have isolated the problem exclusively to Kana himself.
I zoned into Cad Nua. I pressed the key to have the party management window pop up. I removed EVERYONE from the party. It showed them being dismissed, but they remained on the main window screen and I could still select them. I IMMEDIATELY, with only the main character selected, clicked on the map icon and zoned to another area.
I was then alone with my character. I saved my game. I zoned back to Cad Nua. I was still alone. My party members were NOT with me. I then entered the party management again. I added random party members EXCEPT for Kana...and they flashed/teleported to my main character and I had a full party. I did this multiple times WITHOUT Kana with different party combinations. I am now able to change party members at will....but I CANNOT get Kana back into the group. He is effectively stuck at Cad Nua. Whenever I try to add him in with others...he doesn't join, but half of the others do.
Even though I somehow was able to replicate this...I still get a black screen going into the second floor of the Bright Hollow building. I think the two are related specifically because this is the building where your party members go to when they are not with you.
There is something wrong with the Kana NPC and I think its the root of the party management issues.