I could show you a pic of my little bass with bellies bigger then there bodies. Never ever lost a fish from eating to much in one feeding!
Pellets soften right up and wouldn't be like if they eat a rock or something and it got stuck.
Not to sound negative or offend you but I would check over your husbandry again because I have a feeling something is not consistent hence your losses.
I hear ya, I checked everything and he was absolutely perfect this morning. Like I said he was in perfect shape, just dead