It seems like my on-premise V18 Odoo installation did not install properly.

For example: the POS-Module has thrown an error right at installing. A simple retry had shown no error and had the module installed successfully. But after a while, we notice that some buttons are missing. 
We tried to upgrade, remove, reinstall the module, but it just won't appear.

An example would be the customer statement button when looking at contacts. 

My smart button menu: 

What is missing:


We fixed the issues and a new database does not bring up these issues again, but our prod DB needs to be fixed.

Is there a best-practice, common way of fixing such things?