I am currently using Yocto 4.0.14 Kirkstone – Bitbake Version 2.0.0

I am still a beginner when it comes to using Yocto.
The SState cache data is on an internal (HTTPS) cache server.
I would like to use this cache from various devices.
The goal is maximum build security and as much time savings as possible.
What I am looking for is a “best practice” on how to do this.

Up until now I thought that it was enough to set SState_Mirror correctly.
But since I then get this warning:

WARNING: You are using a local hash equivalence server but have configured an sstate mirror. This will likely mean no sstate will match from the mirror. You may wish to disable the hash equivalence use (BB_HASHSERVE), or use a hash equivalence server alongside the sstate mirror.

I assumed that I cannot ignore this warning.

And now I have been looking for a while for what exactly I have to set. I have received various error messages and tried a lot.
With my current settings I have no error messages and no warnings.
I currently have

SSTATE_MIRRORS ?= "file://.* https://xxx`your text`....
BB_HASHSERVE = ""
BB_HASHSERVE_UPSTREAM = ""
BB_SIGNATURE_HANDLER = ""

set.
And it looks like it’s not working properly.
After changing a recipe, it wasn’t recognized that part of the cache could no longer be used and had to be recreated. The Bitbake build aborted. It only worked again after deleting the specific files in the SState mirror cache on my server.

Who has an answer to the question of what minimal settings/configurations I need to make this work?