Two devices unable to co-exist together on a Network

I have a mixed device network consisting of some Windows and some Linux based PCs.

My main PC is Windows 7 Ultimate and there are two other windows PCs, an XP laptop and a Windows 10 Home laptop.

As regards the Linux based PCs, there is a Linux Mint PC (Mint 17.3). In addition, there are two Humax-HDR satellite television tuner/PVRs and a NAS which runs on unRAID.

All devices are set up with fixed IP addresses.

I am having extreme problems with one of the Humax boxes co-existing with the NAS when I am accessing them through my Windows 7 PC. If both Humax and NAS are on, when I try to access the NAS, it asks me for the password for the Humax box and vice versa. If I try to transfer files from my Windows PC to the NAS, it sometimes shows me the folders of the Humax, at other times the correct folders. Partway through a transfer it will say the device is not recognised and then it connects correctly. A few minutes later I lose the connection and it accesses the other device. This behaviour is replicated on the Humax box.

I have confirmed that the devices are all still on their correctly assigned fixed IP addresses. The only way for the transfers to proceed properly is if the other device is switched off. It is only one specific Humax box that is affected this way, there are no issues with the other Humax.

I have the same problems when trying to do transfers using the Windows 10 laptop.

The strange thing is that if I operate the transfers from my Linux Mint PC there are no issues whatsoever. The devices all co-exist happily and transfers occur without problem.

So I can only conclude that there seems to be some Windows Networking issue at play here but I must admit I am totally bewildered.

What are the MAC address for these devices if they are the same that would do it

Finally checked and all MAC addresses are different. In any case, surely it wouldn't explain why it works under Linux and not on Windows.

Are NetBIOS names same or similar?

Sorry, I don't know (how to find) the NETBIOS names, the hostnames of the offending PCs are NAS1 and Humax-HDR.