Dear BRAM,
We did the installation outside the secure network perimeter and as mentioned unmanaged, so firewall is not causing the issue and thing for sure is that we've checked that he can access the Internet without restrictions and freely, why there is no reason that he cannot access mentioned URLs. Also as mentioned, we did the same with the IT computers who loves to work without network boundaries, so diving deep into logs is the next thing to do. However, since we have a jet setter, it's very hard to get in touch or have his unit checked for long a time. Again, it's kinda weird and for whatever reason, is the thing we need to escalate.