An issue was introduced into the java client that prevents it from working with Quarkus. Manual testing is done with Quarkus on a regular basis, and before each release to maven central, but due to a change in process, the manual test was not picking up the latest client jar. Hence the problem was not noticed for a while.

Using a git bisect type approach, it was identified that the issue was introduced in commit c166c26/PR #27, in which the grpc validate plugin was replaced.

Roughly speaking, this issue is a conflict between generated grpc code and the grpc libraries they call, which, although normally consistent, conflict in the case where dependency versions are controlled by the quarkus bom. 

The last released version working with Quarkus is 0.6. The current 0.7 is broken.