Connection leak detection triggered

[ghost]

At random moments, AS will spam the console with "Connection leak detection triggered" errors and request timeouts. While these errors are flooding the console, the server lags severely. It is unknown when the error appears.

The database front-end still works; the database itself is not lagging or freezing.
The server is running a MariaDB database.

Error message:

Connection leak detection triggered for org.mariadb.jdbc.MariaDbConnection@7d70e1c, stack trace follows:

Pastebin: https://pastebin.com/KZgKKBMu

[LemADEC]

Check your database connection pool and running processes