It's been awhile since I last did this but, the New Romulus mission "The Power Source" seems to be bugged.
This particular character is a 23c temporal operative which may be contributing to it but I can't say that for certain.
Upon entering the ruins (at the door it says "Begin Power Station Instance", the instance objectives start but the "Power Source" quest marker stays at the doorway. Moreover the interactive option "Exit Caves" stays onscreen the entire time.
I've tried:
Dropping the mission and re-taking it
Going in with environment suits equipped
Going in with environment suits unequipped
Ensured to watch the "Latest Findings" mission/cutscene that sets up the backstory.