First of all: happy holidays

I have an issue for the past month or so, transmission or airsonic is regurally killed by DietPi.
When searching the logs, I found out that it's because the system is out of memory.
This leads me to this question:
what can I do?
- to understand why it is running low?
- to find a workaround?
I'm using an Odroid C2, with last version of Dietpi, and using proftpd, mariadb, php7.4, apache2, transmission, airsonic, medusa, jackett, syncthing, webmin, fail2ban, rsyslog.
Thanks!