How to debug internal 400 errors in Google Cloud
The error can mean several things. It will help if you can share the request you are sending (without any sensitive data).
Additionally it could be the case that they are DELETE or GET requests with body to a ingress resource (HTTP(S) Load Balancer).
In case of DELETE requests with paylaod, it is working as expected as mentioned in this doc.
In case of GET requests with payload, there is an ongoing feature request to allow them.