try connecting to the QV server directly from QV Desktop on the NP machine. If that works it is not firewall.
Also enable more detailed logging. Hopefuly it will give you more information. https://help.qlik.com/en-US/nprinting/17.3/Content/Troubleshooting/Troubleshooting.htm
I had similar problem with generating cache when I used QV Desktop 12 on the NP Server to connect to QV11.2 sever.
After I downgraded the client the cache is generated without problems (it seems that the SR Version does not have to be exactly the same).
I have installed QV desktop 12.1 SR 3 installed in NP machine and I have successfully managed to connect it with QV server with version 12.0 and also I followed the steps mentioned in the below link where they have mentioned the three things
1) NP user should be in the Qlikview Administrator group in the QV server
2) NTFS authorisation needed to be checked
3)QV desktop should be licensed version
I am able to connect to the QV server through QV desktop using qvp connection
Thanks & Regards,