I had a bug where my Iron Banner quest just disappeared, I have just come back to playing so I had to get to a certain light level to be able to see the IB challenge, completed the challenge and it said to return to Saladin for an engram so I did that, and then the quest just vanished so It can't be completed. Also I've encountered numerous bugs in Spark game mode and these range from the spark just doesn't respawn and you have to just play down the timer (this also means that say the score is 3-2, there is no way the losing team has a chance to win as no spark) and there is another bug where it just constantly transmats you, again if this can cause an unavoidable loss, normally it transmats maybe 5-8 times or something in a row and eventually it just ends the game, so you still get your rewards etc, but it is a bit annoying. I don't play this game much so my opinion probably doesn't count for much but Iron Banner has always been my favourite activity, and I love the armours, so I think for me, the worst part is it can really hinder your progress in terms of the armours, especially as it's a limited time event.