*edit: Turul is right.
Probably there was a non-iron-fist attack tile out there too, disabling IF’s passive.
I was using him with psyduck and blade. All other times even with their black and pink attack tile out, fist’s green attack tile would activate after it was matched away.
I’ve been having this problem as well, in almost every match.
(PASSIVE) The Immortal Iron Fist has the best Kung-fu. So bring it. At the beginning of every turn, if there are no friendly Attack tiles, create a strength 60 Green Attack tile.