So, if i try spawning a player named "a" the game says An unexpected error trying to execute that command ( as shown in this image) must say, that players like "1" "c" "b" are spawneable, even accounts named "sldgfsdkb2490320nsvf" with random names are, i think i spawned "a" once in my world, and i don't know what happened, it was A LONG TIME AGO, like at least 8 months, so, maybe it has something to do with that ( i am not sure if i spawned him once, this is a supposition)
https://imgur.com/a/67R9kjg

Can you please run the following commands in that order and post the resulting log output?

kill a
carpet superSecretSetting true
player a spawn

Cannot reproduce in current versions.

Going to close this as resolved, though open a new one or ask for reopening if it becomes one again.