Upgrades to istio / authservice cause redis to go down for several minutes

When upgrading from 1.8.4 to 1.9.7 of istio, authservice's redis goes down in the cluster for several minutes. Eventually it resolves itself.

@stas investigated this and concluded this was there before 1.8.4 and was not related to the envoy filter changes put in place for 1.9.7.