Execution failed due to configuration error: General SSLEngine problem

When I configure a vpc proxy in the api gateway I always get the same error when pointing to different https endpoint. I have tried amazon.com and various others which all have valid certs. The vpc call goes thru a nlb which is using tcp as protocol so no tls termination should be handled here. It's very hard to see what the problem is with that error message, don't have any clues on how to fix this or to be able to get more detailed information.

Anyone have any idea on how to solve this or at least to get some more detailed error messages?