There is clearly a huge penalty for a user to miss/forget to join a GAC round in the 24 hours given before 'player lock'. But now that CG has made it so that the roster locks when you hit Join and there is no way to unjoin, players have to balance the risk of locking too early vs missing it altogether. For example, I locked this morning because I wasn't sure I would be able to get on again between then and player lock. But I did have time and also unlocked a 7* Negotiator as well thanks to TB. But oh well, no 7* Negotiator for me the next three matches.
Please implement an ability to relock roster, or unjoin and rejoin like we can in TB. I'm surprised this need was not predicted when moving roster lock from player lock time to join time was implemented.