Random "upstream connect error or disconnect/reset before headers" between services

So, this problem is happening randomly (it seems) and between different services.

For example we have a service A which needs to talk to service B, and some times we get this error, but after a while, the error goes away.

When this happens, we see the error log in service A throwing the “upstream connect error” message, but none in service B. So we think it might be related with the sidecars.

One thing we notice is that in service B, we get a lot of this error messages in the istio-proxy container:
[src/istio/mixerclient/report_batch.cc:109] Mixer Report failed with: UNAVAILABLE:upstream connect error or disconnect/reset before headers. reset reason: connection failure

And according to documentation when a request comes in, envoy asks Mixer if everything is good (authorization and other things), and if Mixer doesn’t reply, the request is not success. So that’s why exists an option called policyCheckFailOpen.
We have that in false, I guess is a sane default, we don’t want the request to go through if Mixer cannot be reached, but why can’t?

disablePolicyChecks: true
policyCheckFailOpen: false
controlPlaneSecurityEnabled: false

NOTE: istio-policy is running with the istio-proxy sidecar. Is that correct?

We don’t see that error in some other service which can also fail.

Another log that I can see a lot, and this one happens in all the services not running as root with fsGroup defined in the YAML files is:
watchFileEvents: "/etc/certs": MODIFY|ATTRIB
watchFileEvents: "/etc/certs/..2020_02_10_09_41_46.891624651": MODIFY|ATTRIB
watchFileEvents: notifying

Can anybody help us with this?