Merc wont join me in maps

So ive spent this morning farming a new merc, when I have come to use him finally he wont join me in maps.
things ive checked:
Im level 94 he is level 83
he isnt dead
other mercs will join me on the same maps
things ive tried:
full restart
multiple different maps

really not sure what else to try.

Kind of feel personal that he wont join me in maps lol