I've submitted a support ticket in game and also replied to a post in this forum and still haven't heard anything.  So I'll make my own bug post.

I cannot fuse Justiciar for the progress mission.  I have each of the characters ascended and unlocked.  This is hindering my progess...couldn't use the sacred that I am due for this mission for the last event.  Can't progress on further missions.  

This has evidently been on ongoing issue for a lot of people and is still a problem!  I've spent quite a bit of money on this game and I'm very disappointed in the lack of a response and the ongoing issue that hasn't been fixed.

in game id - um17470674 | 17213911