Axolotl spits out food, it's been 2 days

Hello! I have two little axolotls (around 8 cm each)
I've been feeding them half a small earthworm/ a quarter of a large earthworm each everyday

I've bought some earthworms (the regular ones, not red wigglers) from a local breeder, one of them is eating them just fine but the other one is spitting them out. This is the same Axolotl who had threw up gravel stones (from the petshop tank) some days ago, though he's been eating earthworms just fine until now.

He's not ignoring them, he just eats them, spit them out, then go eat them again, and then he spits them out again, in a continuous cycle until the other axie comes over and eats it himself!

I'm really worried because it seems he's hungry but he cannot take them, I've already tried cutting up the worms in little pieces but so far he's just taken one of these, the rest he just spits them up.

What should I do? Should I isolate him to see if he can finally eat the worm after many tries?

I should also note he doesn't seem full.

Have you tried any other food to see if he still does it? Frozen blood worms? Pellets?

They don't like pellets, in my country no one sells frozen bloodworms, only freeze dried bloodworms

Well it seems he accepted a 1/4 of a medium/small thin earthworm, so there's that.
I've seen him try to throw up a couple of hours before finally accepting the earthworm
Hopefully he's recovering from whatever it is