So this occurred yesterday after the maintenance and apparently, you could only invite 1 person to the party. Anything above that the client will prompt a message that you could not invite anymore.
We also tried forming a raid, there we were able to party as 5 but the amount of EXP given to us is way too low for what it should be. We also tried kicking 1-2 members just to test out and the EXP given went a little higher, I'm talking about from 10-15 MP per kill. We were in the Forgotten Payon map doing Khepris and Tigers while testing this all out.
I saw that there was an update and not sure what was it about but it turns out this bug hasn't been fixed yet so I decided to post this out here.