SSRS 2017 add datasource “Something went wrong”

when trying to add, view or change data source(s) in SSRS 2017 I get popup saying "Something went wrong, please try later".

Setup os SSRS is as follows:

three SSRS instances behind KEMP load balancer. Communication from clients to KEMP is done over SSL (port 443) and from kemp to SSRS instances over HTTP (port 80). rsreportserver.config file has this tags on all three SSRS servers, where SSRS.domain.com points to the KEMP virtual IP (for client access).

SSRS.domain.com https://SSRS.domain.com/reportserver

When I try to add, view or change data source(s) I get this error in RSPortal.log

ERROR: OData exception occurred: System.Net.WebException: Unable to connect to the remote server —> System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it 10.2.17.11:443 at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress) at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception) — End of inner exception stack trace —

10.2.17.11 is the IP of the one of SSRS instances buth what baffles me is why is connection trying to be made using port 443 (TLS) when KEMP is configured to communicate with SSRS instances over port 80.

SSRS instances don’t have port 443 configured, only port 80.

Everything else works fine, only datasources are the problem.

SSRS version in question is 14.0.600.1109, native mode.

Any help would be appreciated.