I'll have to agree with it being a super obscure glitch.
From what I can tell looking into the error message further, it appears that for some reason the blob forgot its own unique 'instance id' upon hitting the floor which caused the 'delete' event to fail.
i.e. Steve hit the floor and must now delete himself, but, for some unknown reason he also forgot that he IS Steve and then when told to 'delete Steve' he just freaks out not knowing who Steve is.
What I don't know is why this happened at that point and only that point in the game. I guess from the fact you made an attack shortly before, that its possible hitting a blob at the exact frame it hits the floor could cause some weird interaction... I'm not sure, and further testing by deliberately hitting them as they hit the floor still doesn't produce the glitch.
Its also possible its a bug in game maker as an update for the engine dropped shortly after I released the game, I've installed said update just in case and will release a new version of the game after the jam finishes on the off-chance this solves it.
Either way, thanks for the extra details I'm sure they'll prove useful should this bug pop up again.
btw the game does save when resting at a bench, so if you want to play more you should be able to continue from your last used bench.