"Secrets of the Ancients" is Bugged [Solution]

I had been stuck with this mission in my list for a year and a half before just completing it yesterday. I had submitted a ticket twice starting about 1-1/2 years ago and no solution was offered relating to those tickets. It was only after submitting a third ticket a few days ago that the correct solution was proposed, yet the mission is still bugged. It took about three additional attempts to complete. I post this in case anyone else should befall this "trap". I'll explain:

The mission requires you to go into the underground caves at Hwael Ruins on New Romulus. There you interact with the usual consoles, scan items, and kill things. When you finally clear everything, you get a popup telling you you're done and a button like "Leave Caves".

DO NOT click the button because the next objective in the chain is to "Signal D'Tan" and guess where you have to be to do this? Yes, in the last room of the caves where you can't return once you exit. To make things worse, the "Drop" button in the mission log is grayed out so you can't drop it. What you must do at this point is look for the mission under the New Romulus episodes called "The Power Source" and REPLAY that mission. This will allow you back into the caves but this is not at all obvious.

You must complete all the objectives again, but not click the "Leave Cave" popup when it appears. There is also no marker of any kind that tells you where this Signal D'Tan popup is triggered, just a giant circle around the entire largest room in the caves. You pretty much need to walk around in the room aimlessly until you hit the right spot. Then the popup appears and there is this very long cut scene and you're done.

I hope this will be fixed and hope this helps someone else.