MetaMask uses passwords in a way that you may not be used to. This mainly has to do with the fact that MetaMask is a non-custodial wallet; it's not a conventional cloud-based app where we keep track of your username and password. You keep track of your Secret Recovery Phrase, and each time you restore your wallet using your Secret Recovery Phrase, you set the password for that specific instance of MetaMask.
This means that if you use different passwords for each instance (Mobile, Extension, Extension on different computers), you need to remember which password you used for each instance.
There is one notable caveat to this: If you have synced your Mobile app with MetaMask Extension, your Mobile password will be overwritten by the password you had set in the Extension you used to sync.