Oh absolutely. This has been a non-stop thing the last 3 days. It's an exciting exception when I end up in a dungeon with 4 other people of the correct roles. The norm is 3 people or 5 people but there's no tank. That's my "favorite"; end up in a dungeon with only 4 people, sit around waiting for the 5th slot to fill with…
The issue appears to be that people queue up but then for a variety of reasons they reject the auto invite. The game then (in a complete "screw you" to all logic) tosses all those who did accept into a party and loads them into the dungeon anyway. What it should do is say "Hey, sorry, somebody didn't accept so you're back…
This fight is 100% impossible to do if 2 out of 5 on your team are HAMSTER. Sadly my two friends and I always get 2 HAMSTER. If you can't get people to actually attack the mystics you just can't win.
This is the first downtime I've run in to that wasn't a pre-announced maintenance. You're magnifying a few bad spots you've experienced and eclipsing what's actually going on.