Where are you using the Primary Password ?

The PP is only used to unlock the passwords stored in the Lockwise Password Manager (about:logins) and not for other case like accessing your Sync account.

I want it to unlock my passwords stored in the Lockwise Password Manager. The primary password that had been working suddenly stopped working and there does not seem to be a way to recover it or make a new one without already having one that works.

You can try to login or logout or change the PP in the security device manager.

• Settings -> Privacy & Security
  Security -> Certificates -> Security Devices

In the left panel select "Software Security Device". You can find "Log In" and "Log Out" and "Change Password" in the very right panel. You may have to Zoom out the page to make this right panel visible.