@jbl85 Are these Windows 11 machines?  If they are there is a bug introduced in 24H2 that killed file sharing between computers.  If not 11, double check your advanced file sharing settings.  Its possible that with the new router, your network settings go changed from a private to public network and turned off network discovery.

  @DVair 2 Windows 10' and 2 Windows 11's.  Had upgraded to 11's 24H2 some time ago and never had an issue after that upgrade.  The issue happened right after I upgraded the router.  So I went into each machine's net settings and reset the network discovery, file and printer sharing, and the problem slowly went away one machine at a time.

So these machines, if they don't recognize the new router, lock down network discovery, file and printer sharing?  I guess it makes sense security wise.  Thanks for your input.

  @jbl85 There was actually a recent Windows Update that changed many network settings from private to public.  I had to go to three different machines and set them back to Private.

  @DVair I get if the problem stemmed from a recent Windows update, but the file sharing stopped the very instant I swapped out the old router for the new. So something else had to be going on. Because if it was a Windows update I would have noticed the problem as soon as Windows update ran, wouldn't I?

Not trying to be confrontational mind you, and don't want to be labor the issue, but just trying to figure out what may have happened.

  @jbl85 I understand, I was just mentioning about the update issue as that was what caused me issues.  It was most likely the new router as Windows saw a new network and the machines turned off network discovery.