-Went in with all 6 event legacy weapons in my inventory, nothing.
-Girlfriend came in with one of them equipped and riding the event speeder, nothing.
-Did introspection and /meditate, nothing.
-Went in with no buffs, not even a form or sprint, and nothing.
-We could not duel in the cave.
-She entered the cave with only her (legacy event) weapon equipped, nothing
-When I entered the cave while she was on her speeder to it, she got the message on her screen as well. When she entered while I was already in it, I got the message on my screen as well.
Another clue! Dagobah episode 5, Luke's X-wing crashed into the swamp, probably ending up in as bad condition as your girlfriend's speeder. Maybe there an event-like speeder that drops off the final boss TFB HM? Sort of like the EC Praxon Bloodline?
Best of luck to you!
...really wish I got that speeder, instead of going my tokens to my girlfriend so she can buy 2...