Okay, so I was playing free play and ran into this issue.
I left the area and went north where there were some scar and dominion fighting. Killed both of the factions and then got some dialogue, went back to area where the event was occurring, then the last dominion spawned. Let me know if this works?
April - last edited April
Happend to our party yesterday evening. Event popped up at the Fortress of Dawn ruins, we kept the area free of scars while the cypher was hacking the link, then once this was done, we gathered 2 of the 3 intel and waited for the standard "Dominion_Thoughguy_001" to spawn with the last bit of intel, but he never did and there was no waypoint indicator to a 3rd pick-up point. Eventually we just moved on to the next world event, since we could all live without the 5 embers the chest would have given us anyway
I can confirm that leaving the area of the event for a few minutes then returning does cause fix this issue... IF it doesn't delete the event completely, though that does not seem to be an issue with this particular event very often if at all. If you're lucky, you will get this event near a couple of hidden places, which you can also use to "reset" the third intel by going in and coming back out.