Board Thread:News and Announcements in game/@comment-34703507-20190518071735/@comment-36219101-20190520090407

I believe it treats it as you've finished every fight twice, so for example say you got a training item in one fight and gems in another. You should get both rewards with the boost feature too.

I could be totally wrong on that as I've only used the boost feature on dokkan events, oof.