I could increase the RAM to see if that helps.
Regardless if it is what's causing the issues you're currently facing, I'd definitely get more RAM if I were you.
Each instance of Mastodon needs at least 1.5GB and each instance of Discourse at least 2GB. Already that is at least 10.5GB RAM you need before you've included all your other apps plus Cloudron and Ubuntu themselves.
And these are bare minimums. If you have users actually actively using these apps they'll need more.
We know this and monitor daily, and we have software that lets us know that RAM needs to be increased whether it is on a server level or on an app level.
We upgrade as and when needed, We also use throttling so if extra RAM or CPU is needed it is given until we decide on its upgrade needs.
After testing it had nothing to do with CPU or RAM it seems to be networking or a service possibly.