We've seen a few reports of this and are looking at the map to see what's happening.
You need some way to give an idea where to go to find the archaeologists.
Additionally, like so many other fleet encounters people coming in late are cut off from the main group by swarms of fast-respawning mobs. This is not an issue unique to this encounter but given it seems to be a theme with you guys, someone should be questioning the design of said encounters for the future.
Saw this bug also yesterday. Scanner showed last archaeologist in hillside by triangulation. I finally just selected a new instance. First new instance was empty, second one was still finding the archaeologists but all were found (the last one wasnt in a hillside in this instance) and we completed the Dig.