OK so I must be really dumb. I had a red alert come up and joined it, selected the mission, and the I found myself back in sector space having never seen a Borg. What did I do wrong / what should I have done? The mission still shows up as needing to be completed.

Thanks in advance for the help.

might have just bugged out on you.

basically when one appears you have about 10 minutes to enter. ideally enter as soon as but its not always critical.

then you should be placed in an instance with several other people. it should be 5 max but its a bit buggy and letting in some big fleets.

in a nutshell just try it again and you should be fine.

Same thing happened to me..clicked on the red alert..took me to the Borg Front, selected the mission, even received the 5x XP bonus item, then it dropped me into sector space again. Hopefully they will fix it with the patch this morning!