Syndicate member missing.

Ok so ive been messing around with the syndicate combinations and what not trying to get used to moving who i want to put where ubt now hillock is missing. normally when i press remove from syndicate they just turn into little blue question marks but now hillock is compeltely missing and i havent fought him seen him or anything for about 8 days or so. im not sure how this happened or when exactly. ive asked a lot of people and they jsut tell me " he will come back" yet he never does.
he is still there on other characters as are all the other members but for my triple herald blade votex witch he isnt and i dont understand why.
does anyone else have this problem?