Links in Subscribed Reports using Hostname

I think I found the fix for this. If you look in the most recent ReportingServicesService_<datetime>.log file I saw lines like the following:

configmanager!WindowsService_0!134c!05/29/2019-09:20:49:: i INFO: Using report server internal url https://<server FQDN>/ReportServer.
configmanager!WindowsService_0!134c!05/29/2019-09:20:49:: i INFO: Using report server external url http://<server machine name>:80/ReportServer.

Notice that the external url is listed as being the machine/hostname.

It's not very well documented (in fact the docs claim that its only Sharepoint that uses this setting) but I found that adding both ReportServerUrl and ReportServerExternalUrl settings in the rsreportserver.config file fixed this issue.

These setting needs to be nested in the <UI> element (see below)

<Configuration>
       ....
	<UI>
		<ReportServerUrl>https://<fqdn>/ReportServer</ReportServerUrl>
		<ReportServerExternalUrl>https://<fqdn>/ReportServer</ReportServerExternalUrl>
		<PageCountMode>Estimate</PageCountMode>
	</UI>
       ....
</Configuration>

After adding these settings I think you need to stop then start PBIRS for them to take effect. Make sure to take a backup copy of your config file and check the most ReportServerService_<date>.log file after re-starting PBIRS as if you introduce any errors PBIRS may not start up properly, but you should find the reason in this log file.