Hi,
How it has been narrowed down to one server? Any errors on the load balancing or events?
Please provide the error message in OWA and ECP when it’s not functioning? Based on that we can check the configuration.
Else, you can also try re-creating the OWA and ECP virtual directories with default settings.
https://theitbros.com/recreate-owa-ecp-virtual-directories-exchange-server-2016/
https://learn.microsoft.com/en-us/exchange/clients/default-virtual-directory-settings?view=exchserver-2019
If the above suggestion helps, please click on “Accept Answer” and upvote it.