Exit Status: 48 (client hostname could not be found)

Is status 48 now resolved?

For some or other reason I got distracted from original status 48.

'Client hostname not found' is resolved by adding client IP and hostname to DNS or to master and media server's hosts files as well as double-checking policy for typo errors as far as Client hostname is concerned.
After changes to hosts files (or DNS) were made, refresh NBU host cache on master and media server:
bpclntcmd -clear_host_cache

Status 25 is a separate issue and points to port connectivity.
You have selected NBU 7.5 in your opening post.
If this is correct, you ONLY need port 1556 between master and client as well as between media server and client.

Check that bpcd and vnetd processes as well as pbx processes on the client are running.

This points to problem on the client:

 status: FAILED, (42) CONNECT_REFUSED; system: (10060) Connection timed out.; FROM 172.20.124.11 TO BEC13-ENC2-2 172.20.165.4 bpcd VIA pbx

Please confirm the NBU version on the client as well as processes running on the client.

Do the following from master and media server:

bpstestbpcd -client <client-name> -debug -verbose