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I might be wrong on this but...
After running composer, did you have to go through an install process? If so, the DB/site you were given might have been configured to use a database table prefix.
If you look in your database, do you see some tables call assets then a second one called xxx_assets (xxx_ could be anything)?
If so, in your .env file, make sure have DB_TABLE_PREFIX= set to whatever prefix (the xxx_ part) you are seeing on your tables.