computers missing in network

Hey everyone! My first post here - I usually just glean what I need from reading other's questions - this one has me stumped, and I'm hoping y'all can help.
Our home network consists of
2 fresh-install win 10 1909 PC's
1 v 1909 that has been part of the network and is NOT a fresh install
1 Win 7 machine that has been part of the network
The main function is file transfer for streaming on one device or another, as well as general data storage. Previously, everything was working fine, until I tried to integrate the two fresh installs.

After sorting through various password problems, I managed to everything talking a couple of days ago.

Today, I was able to see all 4 devices and was successfully transferring files from the 7 machine to my non-fresh-install when the two fresh installs disappeared from my "network" screen.
No matter what I did -
Followed "Share Files and Folders Over a Network in Windows 10"
and Fix: Network Computers Missing in Windows 10 1803 Version 2018 ),
Restarted
Rebooted the router (Google Mesh)
I can't get it to show those devices. One fresh install computer can still see all network devices, however the others can only see a couple.

Now, the one that I've been transferring files from (Win 7 machine) has disappeared - says "not connected" however I have a window open that is still fully connected to that computer, allowing me read/write permissions.
One of the fresh installs can see all network devices.
The other fresh install can only see the 7 machine.

What am I missing, before I pull all of my hair out??
Thanks!
Bess