I have had this issue on the $5 droplets on DO as well. There are two fixes that have worked for me and proven to be reliable fixes.
PROBLEM: Mysql container is killed and when listing docker containers (docker ps) you see the mysql container perpetually restarting. Also checking the system logs surfaces error messages that essentially indicate that the droplet is running out of memory and the most memory intensive containers will be killed. That is always the mysql container.
EASY FIX: In 100% of the cases for me, I upgrade the container from a $5 to a $10 month container, making sure to select the configuration that effectively doubles your RAM memory. Problems solved. But of course, that will cost you more per month.
CONFIGURATION FIX (a bit harder): For those droplets where i just don’t feel like I wish to expend the extra money per month, like low traffic affiliate sites, I wound up taking the relevant parts of this article https://easyengine.io/docs/prevent-mysql-crashing/ and this Github issue https://github.com/EasyEngine/easyengine/issues/791 and made the configuration changes manually. I have to check to make sure those changes stick after upgrades and updates but since I placed the files in the recommended global folder /opt/easyengine/services/mariadb/conf/conf.d/ I have not seen any of my modifications change.
If you prefer to run a well known script to get some optimized settings, check out https://easyengine.io/handbook/how-to-use-mysqltuner-with-ee4/ and ticker with mysqltuner. I have used this perl script many times on larger traffic systems, but rarely mess with it on smaller sites. it just seems easier to mess with the max_connections and the various timeouts manually. Sometimes the output from mysqltuner gets a bit involved and can actually cause more issues if you do not know what the settings actually do to the site.