brianrlawson yep, I confirm that your Mastodon is app exceeding your memory allowance and that's causing your processes are being terminated.
You might be able to reduce Mastodon's memory usage (at the expense of performance) by adding the following to your app's mastodon/.env.production
file:
WEB_CONCURRENCY=1
Be sure to restart the app after updating the config by executing the following command:
~/apps/your_app_name/restart
I think this might work for you, based on our system logs you were just over your quota. Your app's 2 web server processes are running about 200MB each, so by setting the concurrency to 1 you should gain about 200MB of breathing room.