I have a MariaDB on Debian 8 and have an issue with luckpems. In config Id chosen MariaDB.
Using bungee, but error not even on proxy

[06:29:54 WARN]: [me.lucko.luckperms.lib.hikari.pool.PoolBase] luckperms-hikari - Failed to validate connection me.lucko.luckperms.lib.mariadb.MariaDbConnection@4bc16f38 (Connection.setNetworkTimeout cannot be called on a closed connection). Possibly consider using a shorter maxLifetime value.
[06:29:59 WARN]: [me.lucko.luckperms.lib.hikari.pool.PoolBase] luckperms-hikari - Failed to validate connection me.lucko.luckperms.lib.mariadb.MariaDbConnection@592a80c1 (Connection.setNetworkTimeout cannot be called on a closed connection). Possibly consider using a shorter maxLifetime value.
[06:29:59 WARN]: [me.lucko.luckperms.lib.hikari.pool.PoolBase] luckperms-hikari - Failed to validate connection me.lucko.luckperms.lib.mariadb.MariaDbConnection@29d576f7 (Connection.setNetworkTimeout cannot be called on a closed connection). Possibly consider using a shorter maxLifetime value.
[06:29:59 WARN]: [me.lucko.luckperms.lib.hikari.pool.PoolBase] luckperms-hikari - Failed to validate connection me.lucko.luckperms.lib.mariadb.MariaDbConnection@10bd968b (Connection.setNetworkTimeout cannot be called on a closed connection). Possibly consider using a shorter maxLifetime value.

https://hssteb.in please

https://pastebin.com/PBBCFq76

There's some useful info for you here: https://github.com/lucko/LuckPerms/wiki/Storage-system-errors

:)