As pointed out by @mattklein123 in msample/envoy-filter-example#1 there is a bug in the grpc AsyncClientStreamImpl here:

https://github.com/lyft/envoy/blob/master/source/common/grpc/async_client_impl.h#L49

Using is RpcChannel instead of AysncClientStreamImpl is a more tested but deprecated alternative. Ideally AsyncClientStreamImpl could be fixed instead.

SEGV caused by this bug can be reproduced by following instructions in msample/envoy-filter-example#1