We are experiencing similar behavior after implementing a privatePortalURL using the format: https://LoadBalanceURL.domain.com:7443/arcgis
This is a 10.9.1 HA deployment with two portal servers, two federated servers, and one web adaptor with IWA. F5 is the load balancer.
Federated servers will validate successfully off and on. We are also seeing this with publishing hosted feature layers and deleting items. The inconsistences came with setting the privatePortalURL.
We've tried turning off one portal machine to see if that clears up the issue but no luck so far. No blocks encountered in the firewall that line up with the errors we see in Portal.
Error messages include:
Could not connect to the ArcGIS component at URL 'https://LoadBalanceURL.domain.com:7443/arcgis.' The ArcGIS component on that machine may not be running or the machine may not be reachable at this time.Error: Connection reset.
We've opened a support case to work through the issue.