UUID Trouble

My server has been experiencing weird things with UUIDs. For example, I set up all player data, and permissions and they were working properly, but they are not working at the same time. I have come to the conclusion that it has to do with UUIDs since at first one of my admins did not have perms, but everything was right in the config then when I gave him admin perms he got a new UUID.
Example:
OLD DATA for Kri0s_CS:
“3329fb6d-306f-433b-baf8-e230e3fc915b”: [
{
“parents”: [
“group:admin”,
“group:MVP”
],
“options”: {
“name”: “Kri0s_CS”,
“prefix”: “&4&l{Head-Mod}”
},
“permissions”: {
“pixelextras.command.pc”: 1
}
}
],
NEW DATA for Kri0s_CS
“c00efe12-68b2-3e81-b1e1-8a456c6c50d8”: [
{
“parents”: [
“group:admin”
],
“options”: {
“name”: “Kri0s_CS”
}
}
]
},
This bug (at least in my uneducated opinion) is impossible since Mojang stores UUIDs on their servers, so if you have any ideas on why this is happening then, please help.

Is the online normal UUID for Kri0s_CS Minecraft UUID / Username Converter

Using the username Kri0s_CS in an offline UUID generator: Minecraft Offline UUID Generator | Minecraft Server List

Outputs the UUID c00efe12-68b2-3e81-b1e1-8a456c6c50d8

If you are running your server in offline mode, this is why.

If you are running a bungeecord setup, make sure they are connecting through the proxy, and that IP Forwarding is enabled for the server both on the proxy, Sponge configuration, and that the BungeeCord module is also enabled on the Sponge config.

IF you arn’t running in offline mode, Arn’t running behind a bungeecord setup, and arn’t running a cracked server of some kind, then you are encountering a bug and some more details would really help.