Went through your steps:
Where the Kibana Instance works; they use Firefox. Went to Kibana and refreshed the page. It shows things are properly being cached. However I do not see the core.entry.js asset (not sure if that's a "problem")
Where the Kibana instance does not work; they use Chromium. When I go to Dev Tools -> Network there is no specific "Transferred" tab. However, I can refresh the page and look at the Headers for each asset. Looking at the Response Headers section, about 90% showed:
The remaining 10% showed:
I also do not see the core.entry.js here either.
Does this information help or give any additional insight???
As far the clusters go, they are identical in configuration. Traffic is routed the same via Filebeats. Config and yaml file are structured the same. They have identical indices and index mappings. They were designed to mirror each other as much as possible.
The main difference is the site where Kibana DOES work is the location that receives ~10x more data. This is why seeing Kibana Requests and Connections at a much higher rate at the "smaller" location confusing- especially with much less data and the constant issues/errors.