RE: XPS 8300 Windows 10 Broadcom network adapter disconnect FIXED
I reworded my original post to make clear that the network and everything is working fine in Win10 now. I'm glad it seems to be working for others too.
This exact problem also seems to be happening on other Dell PCs with a Broadcom adapter. I've seen reports of it on the Inspiron 580 too. Hopefully installing older drivers fixes it for others as well.