Bungeecord
Spigot 1.8.8 (Lobby)
SpongeForge 1.10.2

Authme + FastLogin

I have ChangeSkin on all of them with the same config (same mysql database), but only players who have Premium accounts have skins.

I don't know if it's relevant, but in the lobby console I get this everytime a player logs in: https://hastebin.com/zowisuwosu.vbs

Ok the skins are working in the lobby, just not on the sponge server...

https://hastebin.com/eyuwirajiy.scala

SpongeForge doesn't include the driver of MySQL. It includes the one of MariaDB a fork of MySQL. You should able to switch without any issues just change the driver to org.mariadb.jdbc.Driver

Should I switch the spigot server and bungee to mariadb too?

No only sponge.

It works... It would be nice if this was in the default config file.. It doesn't make any sense to come with a default driver that does not work...

Thank you :)