Make sure that you do not confuse the Primary Password and the password of the Firefox Sync account as both are different and have a different purpose.

The Primary Password is only used locally to encrypt the logins stored in the profile folder and is never part of Sync and each device can have its own PP apart from mobile devices that use OS authentication (face/finger).

• https://support.mozilla.org/en-US/kb/using-primary-password-sync
• https://support.mozilla.org/en-US/kb/use-primary-password-protect-stored-logins

That means something is wrong with the login and the sync is still using the old password on the other accounts. You need to logoff all devices and retry again. And make sure the email registered is the correct login email otherwise if you loose the verification on the old email to the new email then there nothing more that can be done here.

Dropa, Nothing about Sync was mentioned, only about Primary Password.