To make a long story short, my code doesn't compile after the upgrade (after many releases which were drama free). I have put up a demonstration of the problem here:

https://github.com/danielbprice/oapi-codegen-problem

I found that by changing application/problem+json to application/json in my openapi.yaml file, the problem goes away, so I suspect it's related in some way to changes there. Thanks!

Possibly this could be related to what the user in #1146 was talking about. Hopefully my reproducible test case will help.