I‘m facing the same issue - for YEARS to be honest, even back in old owncloud times. I never managed to get other nextclouds to be green.
Indicators:
- my Nextcloud log says „[remote server] refused to ask for a shared secret“ at the time when trying to establish the trust for the first time
- also in NC log: „Remote server presented lower token. We will initiate the exchange of the shared secret.“
- database table „nc_trusted_servers“ contains entries for all remote servers including a token and status 2, but columns „sync_token“ and „shared_secret“ (!!!) are empty“
What else to check or try? Any ideas?