Hi Iñaki,
You're right, even after receiving that email about the token being expired the incoming mail setting is still working fine, so I think there is no technical issue to fix, maybe just changing the oauthrefreshtokenexpired string may be enough; after reading what you said, I suggest something like this:
Current message:
The refresh token for one of the OAuth services {$a->issuer} on your
site {$a->siteurl} has expired. This will limit the functionality of
any plugins that use this service. To fix this issue, visit the OAuth 2
Services configuration page and click on the "Connect system account"
icon in the table row for this service. Be sure to login using the same
service account for the OAuth system each time.
Proposal:
The refresh token for one of the OAuth services {$a->issuer} on your
site {$a->siteurl} has expired. This shouldn't be a problem as long as you receive this email it occassionally and you have the "Refresh OAuth tokens for service accounts" scheduled task running with the default frecuency. Otherwise, this will limit the functionality of
any plugins that use this service. To fix this issue, visit the OAuth 2
Services configuration page and click on the "Connect system account"
icon in the table row for this service. Be sure to login using the same
service account for the OAuth system each time.