new Oauth login with existing LDAP rocket.chat user gives "Email already exists"

[schirrmie]

Hello,
we are currently trying to change our authentication method from SAML to OAuth.
We have Rocket.Chat version 3.13.2 and Ubuntu snap installation.

All Users already have a Rocket-Chat account over SAML and therefore also in the LDAP for Rocket.Chat.
We have successfully implemented a custom OAuth with Azure AD and new users can authenticate themselves over this method. Existing users get the error "Email already exists".

We have already activated the option "merge users", the error stays the same however.

Do you have any recommendations how we can switch to Oauth while keeping our current user-accounts.
Do you need any more informations?

Regards