Hi @Siggg,
Welcome to the Sendbird Community. This is actually expected behavior. Once an access token has been generated for a user, they must always connect using that access token. Regardless of whether the security setting is read&write. Access tokens can not be completely revoked. They can only be revoked and re-issued. In order for users to join the old chat, you would need to have them connect with the access token.
As far as best practice, I’m not sure there is one here. Two different end applications connecting to the same Sendbird application is not uncommon but what is uncommon is each app having different security requirements. It may be best just to loop through your user base and issue accessTokens for all, and implement a way for both apps to utilize the accessToken.
