I have folders on each of my Windows machines, W7 & W10, that are shared and that can be accessed by any of those computers. I routinely copy files back and forth between them, even now. There is even a USB drive that is shared via my router, an ASUS AC1300.
However, when I use my Linux machine, it can't view any of the shared drives on any of the other machines, not even the USB drive on the router, which all worked beforehand.
I have an ac1900 with ddwrt and 2 usb ports that I have 2 ssd’s connected to that can be seen by all my devices, but I don’t run linux except for occasionally playing with linux. It is more curious that your linux os does not see your routers drive - Windows should not even be involved in that, it should be linux os to router - no winos involved...
It might be easier troubleshooting why your linux machine can not see the router usb since that does not involve windows and solving the usb problem has a high probability of solving the windows share problem — in fact you don’t seem to have a windows share problem since the usb on the router is not seen. (btw my ac1900 is Netgear, just to be clear.)