Some members were complaining with bugged ultraxion debuf application indicators.

[Deleted]

Is that common? Can it be remedied?

For example, they would get a warning of getting the debuf every time it was applied to anyone else. When they did get it they would get it with bugged timers or overlapping with another erroneous indication of application.

Me and several other players did not have an issue.

I was on pitbull as raid frames and DBM btw.

[Jacus]

It was very bugged on ptr (showing in buffs or not showing at all) but we had no issues on live. On live DBM was wrong often with the timings but as DBM isn't part of wow, we had no issues with the fight itself.
I would suggest using power auras (http://www.curse.com/addons/wow/powerauras-classic) and setting it up for the Fading Light debuff with a timer, works perfectly every time.

[Deleted]

We had some problems with DBM on the Hour of Twilight timing as well, but aside from that it all went smooth.

[lakhesis]

We had people who weren't having the button show up. That can be got around by simply keybinding it in the default Bliz keybindings (it's called Extra Action Button 1, it's in the Menu -> Keybindings -> Action Bar Functions section between Action Button 12 and Special Action Button 1).

We had people who didn't realise that the 'Fading Light' ability takes between 5-10s to go off so you can't just mindlessly hit it in sync with DBM's countdown, and need to actually watch the timer on your character's debuff (and hence need your addons set up properly to not filter the debuff out... or just turn default bliz buffs/debuffs on).

We had some people who had more significant lag issues on the ability than they typically did with other casts, and so were having to press their button with ~2 seconds left to go rather than timing it right for the end of the cast.

If your issue was something other than one of those, then I didn't encounter it. Admittedly my DBM was working correctly to judge applications and I was calling out all those affected, so some people may have had further screwy addon issues that they tactfully didn't mention & they got lucky on timing while tactfully keeping schtum.