You are welcome. OK, that's clear regarding the computers. It's the Win 10's that fail to see the Win 8.1, but not the other way around. So, that means the Win 10's must be publishing their resources (FdResPub).
(1) It does seem to be a clue that all is well when the Win 8.1 is signed in to an Administrator account. Even though the Standard account is set the same as the Administrator regarding sharing settings, maybe it isn't doing its FdResPub. Or not doing it on time. I know you suspected as much in the other thread. Have you tried restarting it one of the ways fg2001 said in there. Either restart it in Services or use these commands at an Administrator Command Prompt...
NET Stop FdResPub
NET Start FdResPub
(2) Does there appear to be a difference in the status of FdResPub between the Administrator & Standard accounts?
(3) Why not change the Standard into an Administrator this way...?...
(a) Sign in to the Adminstrator account.
(b) Right-click START, & select "Run".
(c) Enter "NETPLWiz" into the run box.
(d) Select the Standard account in the "Users for..." window, & click "Properties".
(e) At the Group Membership tab, switch it to be an Administrator.
Does that fix it?
(4) I'm trying to see in here whether you can keep it as a Standard account & still get published into the network by changing a few settings...
Manage User Accounts in Windows Server Essentials
But that's a tough read. See the section entitled "Understand user accounts".