Why SSAS tries to connect to the default instance?
It would be helpful to know if your running in a Clustered environment or not. However here are some suggestions:

1) Make sure that SQL Browser service is running and that the service user has local administrator rights (Local System Account). Please note that SQL Browser service listens for client requests on port 2382 and then redirects the client connection to the port used by SSAS instance. (In your case it would be 2383)

2) If Analysis Services is running on a Windows Server Failover Cluster (WSFC), the SQL Browser service has to be started on all of the nodes of the WSFC

3) The port information for the instance is relayed by the SQL Browser services only if property InstanceVisible is set to 1 (true). Verify this under General / Advanced settings of SSAS.

4) Test for connectivity by using the telnet command: 


  TELNET InstanceName PORT


If you get a "Could not open a connection to the host, on port" error message, it could mean that the instance is running on a different port or something is blocking access to this port.