1) The described below bug happens only on 1 of my characters.
2) When I try to join any premade (cele/ordos usually, I dont need anything more on that char), I get the leader as battletag friend, I get in the premade list, but I dont receive the invite in the party. So I have to whisper the rl, and the he in 30% situations understands me, and in 70% just ignores. What can be the reason? Could that be some addon conflict? (I do not use ELVUI, I have autoaccept in some addon, but only from guild members).

turn off the auto-accept addon as its obviously receiving the incoming invite and declining it

btw, what addon is that?

I think, in my current config it`s only RBS. Autoaccept is just it`s minor feature.
But on all the other characters it doesnt conflict at all.
I`ll still try to turn this option off, when I`ll have to use OQ on my problematic hunter, but it doesn`t look like this is the reason.
 

On the new week tried turning that option off, no effect. Could you tell me, what configuration files could contain anything about a single character? I`d try to wipe the config on that specific char.