It's pretty unusual to want to run two separate web server frameworks in the same process. I'd certainly expect conflicts – the soundest advice is probably just "don't do this".
A concrete reason for conflicts might be that the two are fighting for a port. Are you sure they are not trying to listen on the same port? Are you sure you are trying to connect to the port that the server (well, whichever one it is you are trying to reach) is listening on?
Anyway, there are more (albeit unrelated) red flags in your code (e.g., in the handler() function, why are you calling format!() if there's nothing to format?), so perhaps a general cleanup/refactor should reveal more potential problems?