The (production?) server is started in development mode. This is problematic as it is doing a lot of overhead processing (looking for file changes), but mainly it’s allowing you to make code changes by configuring content types etc.
When you modify content types, you’re also modifying code. Those code changes are replaced when you upload new code and if one element is out of place it could cause Strapi to reset entirely.
In short, development mode is not designed to run for days and it certainly shouldn’t be used in production.
Change yarn develop to yarn start. See Deployment | Strapi Documentation more details.