You will want to review our linking strategies. When this occurs, oftentimes, this is due to custom mapping needed (you can see this in our discord doc).
https://fusionauth.io/docs/v1/tech/identity-providers/#linking-strategy-examplesThe event log is another great place to look to see how your user is or is not being linked/created.
You can also look at our doc for discord as an IDP
https://fusionauth.io/docs/v1/tech/identity-providers/openid-connect/discordHope this helps!
Josh