Istio, Envoy and bi-directional gRPC question

We are currently using Istio + Envoy + Bi-Directional gRPC Streaming APIs.

We have configured Envoy buffer size ~ 64-128K for our workload.

During Istio + Envoy upgrade, Envoy buffer gets wiped out and the data is lost, considering that client is unable to do retries in certain cases.

Hence the question is: does Envoy support persistence to the data in this buffer or is there any plan for it in the future?

If not, any recommendations on how to avoid data loss during Istio upgrades ?

Checking again, if anybody has any recommendations ?