Comment 7 for bug 1754345

To replicate this issue, make sure you had at least one update available for one of your snap package, then go to the Ubuntu.com and change your Ubuntu user password! Head back to the terminal and type "snap refresh". You get "invalid credentials" error for any packages that you had installed before the password change. Also all feature updates for packages you had before changing your password give you the same error.
Unfortunately, the only way to fix it for me was to remove all snap package and reinstall it again.
Also, snap logout and snap login after password change does not change anything. You still get "invalid credentials" for all the feature packages updates you had installed before changing your Ubuntu password.
Also, your removing /var/lib/snapd/state.json give you false "All snaps up to date."