I haven’t exactly run into similar problem, but it might be caused: If anyone keep changing the items on the content type model, it will run a migration each time you pull the code and run strapi. Depending on the changes to the models, you can wipe entire tables or fields in a table.
If this is the case I will recommend having some kind of test, commit hooks or github checks to prevent edits to models going live without proper checks. Also having this settings in the database.js config should prevent forced migrations:
Welcome to the community.
Make sure you are not using sqlite as that’s what it sounds like you are doing.
Sqlite database with heroku will reset your database everytime the container / dyno stops and sleeps.
You want to use PostgresSQL etc as a database so the data is persistent.