Keep losing connection to resolve network name to IP with only one other computer

[hucker]

I have 7 Windows 10 PCs on a network, all connected to the internet with a fibre router, which hands out the IP addresses. These IPs are dynamic, but they always stay the same since I don't turn the machines off. The main computer (Windows network name "Ryzen") frequently has trouble connecting to one of the others (network name "black") if I use the network name. Things using the IP work ok (eg. Boinctasks), but things using the name fail almost every day (eg. Windows file sharing and Remote Utilities). If I enter "ipconfig /flushdns" into a command prompt, everything works, until the next day. Why is this repeatedly happening, and with only one machine? It is the oldest of the machines (DDR2 era), the others are DDR3 and 4.