I have two computers set up on Linux. I tried to add a third computer using Win10, and Syncthing assigned it the same local address as one of the Linux computers. Can Syncthing sync two computers with the same local address?
I think the underlying question is “why are duplicate addresses being served and how do I fix this?” as it’ll break more than just Syncthing.
Syncthing relies on the operating system to deal with connections at that level, so if your OS will permit it, Syncthing will use it. If the addresses really are duplicates, chances are it’s not going to be able to connect directly, but may go via a relay or, if discovered, a valid local address.