In most cases it is related to the DBM settings. You can change the settings or disable DBM for a while. There is really nice info on how to adjust the cinematic settings here.
You may also reset the whole game interface if you are not sure what addon may be responsible for it.
In some more rare cases it is also related to the pets. So you want to dismiss the active demon or other pet before that scenario starts.
Also before you reattempt it, please abandon the quest and start it again, to be sure that you are on the right track.