about 20% of players not able to join my azurite mine

bug number if relevant: 1,125,105,790

basic rundown: I invited about 45-60 players into my azurite mine for the 6link recipe. 10-15 of them could not join my instance. they would port into an azurite mine instance, but not the one I have open.
is there some kind of requirement to be at the same or similar depth? I'm at 190 and invited people from level 70 to 97 and can't see any similarities between the ones who cant join.

it seems the problem is the blue circle on portraits that port you to someone's location. rather than port them to my mine, it just does nothing or throws up a message saying "cannot join instance" or something. even when I would stand in my mine entrance, it wouldn't let players join with that feature (it worked last league when doing trades.)