your suppose to be able to but it's bugged right now. It was working originally but then something broke it.
Did they break this again?
You're supposed to be able to Rejoin Last Event through the LFG tab.
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I hope they fix it soon. Clicked into a BAF last night, saw the loading screen for it, then the loading screen for the game, then the loading screen for RWZ and I was back where I started, all alone. 
Justice Blues, Tech/Tank, Inv/SS
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Fighting The Future Trilogy
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I used this feature successfully just a week ago. Might wanna retry it.
Currently writings this post after a Mapserver booted me from a BAF Trial. Currently waiting for it to finish so I can join the next. Anyway, I think it's completely unfair that players can't rejoin a trial after a Mapserver, whereas they can after a normal TF.
Any sort of workaround that the Devs can implement?