Zitadel Errors.AuthRequest.NotFound error on production instance

HI there. Maybe anybody can push me in the right direct even if this is very vague. We have two separate instances in Zitadel, one dev and one prod. We basically replicated the setup and users on the prod system. The only obvious difference between the two is that the prod uses a custom domain (which is verified). Now, when a user logs in on the dev system, everything works as expected. The prod one unfortunately throws this error: "Failed to exchange authorization code for access token. Errors.AuthRequest.NotFound"- The first part is from our system, the second part is the error code we get back when trying to exchange the code for an access token. I double checked he actual URL that is called and it looks reasonable. Has anybody experienced this error also or give us a pointer where to look and what could be causing this (some unintentional misconfig in the instance etc that we overlooked...) please?