MariaDB using more than 50% swap memory, even when RAM has sufficient free memory.

Customer's mariadb instance is constantly utilising 60-70% of swap memory on the server, even when RAM is not saturated nor used up to 40%. vm.swappiness is set to 1, and Transparent Huge Pages have been disabled. I have attached and run gdb on the running mariadb process, and would need help from Engineering to take a look at the backtrace generated