My gelding is spitting out clumps of chewed grass?!? Help!?

My horse Psyche is 7 and just got his teeth floated this April, and the horses were just put on pasture, and I noticed he is dropping LOTS of clumps of chewed grass. He’s always been a hard-keeper and slow eater, and I thought getting his teeth floated would help, but it seems to have caused this food dropping!?! This is really not good. He is not thin, but he def. doesn’t have weight to lose. My other horse doesn’t seem to be having a problem, so I doubt it’s the pasture. She’s nice and fat, and got her teeth floated as well….so I don’t think the vet floated wrong or something either. I watched him in the pasture for like twenty minutes, and he grabs lots of grass lustily and chews it up, then chews slower, awkwardly, like it's really tough or something, then just lets it drop out in clumps and goes on chewing and grabbing other grass. I just don’t know what caused this!!?!?! HELP?!?