I'm totally lost

LOl, try the simple approach first, just set the My Cloud as Local Master Browser and reboot everything. Most of the time that’s all it takes. The other method is the the ‘nuke it from orbit’ approach, probably overkill but guaranteed to work

Speaking of rebooting. All this gear needs frequent re-booting (just to clear out any gremlins that creep in.) Doing so monthly will suffice. with all computers, My cloud etc. shut down, reboot the modem and router or combo device. Let it settle in and when it is ready boot up other devices such as my Cloud and computers.