I just finished round 1 in grenade training, he tells me to go again, only I can't re-activate the training.
Same as what you're having. But this happens after the update 1 patch. Even with trainer off, I still have the same problem.
I restarted the mission without the trainer and was able to continue and finish training. The trainer can mess up some missions if particular options are enabled.
I guess I'll have to do that, however I'd like to point out other people have that this problem in Consoles (PS4) from what I've seen. So I don't know 100% if it is the trainer.
Edit: After restarting the mission I did manage to get past it. However now I am stuck in a different level. I am using the WASP to shoot at the guys stopping the truck in Santorini, but nothing happens after that. The van just sits there. If I try killing anyone else the checkpoint restarts. No options activated on trainer.
Edit II: Got past that too after restarting the mission for a third time. No idea what changed.
Edit III: Finished game with no more getting stuck. Decent story.
[Edited by Lizml86, 11/7/2014 10:18:41 AM]