Grpc server with async and sync services at the same time

[Adrian Tut]

I need to be able to serve responses for some particular requests from the main thread, while the rest can arrive from any thread. With that in mind, I created a GRPC server which has 2 services, one is implemented as an AsyncService, and the other as a sync service.

However, when adding a completion queue, the sync service no longer responds to requests.

Is that not supported and if so, what alternatives are there?