Cygames has released a Version 1.0.5 update for Granblue Fantasy: Relink, which addresses the online matchmaking and fixes issues tied to certain quests.
The patch notes on the official Granblue Fantasy: Relink website are quite brief, though the Japanese website goes into further detail. First things first, Cygames has made an adjustment to the matchmaking for online co-op. There is a power value adjustment setting which, when turned on, ensures you match up with other players who are around the same power level as you. From the sound of things, this feature wasn’t working quite as intended as Cygames has “reviewed the matching targets when power value adjustment is set to ON,” so now you should be paired with players of a similar level more often.