Network path not found after 1803 update (Windows file sharing)

Hello!

I have a home network consisting of 3 desktop PCs and 1 laptop. 3 of these are running Windows 10 1803 right now, 1 PC is running WIndows 7.
I just updated 1 PC and 1 laptop to 1803 yesterday, the third one was already on 1803.

Since then, I cannot access my older desktop PC from my newer desktop PC, and I get the infamous 0x80070035 The network path was not found error. There was a not working network discovery issue also, and one PC was on public internet config, but I solved these (function discovery services were off).


So current situation is:
Xeon L5420 PC is reachable from Samsung laptop and Windows 7 PC. Gives error from Dell 3010.
Every PC sees every PC and every other connection works properly.

Dell does see the name of the Xeon PC, but cannot connect, not by clicking, not by typing in \\computername, and not by \\IP-address
Ping of the IP works.

I also tried to delete login credentials, and changed the name of the Xeon PC. I had to type in username and password again on laptop and Windows 7 PC, after that they work again. It still does not work from Dell.

I have tried the common online solutions but did not help. I don't use firewall, except windows firewall which is disabled now. I start to think that the Xeon PC blocks the Dell for some reason.
I really need to make this work, the Xeon shares 4TB data and I use it frequently.

Do you have any idea what to do?

Update:
I cannot ping the NetBIOS name either.

Command on Dell 3010 :Ping request could not find host G41L5420. Please check the name and try again.
Command on Samsung: runs ping correctly.

Also if I mistype the name, there is some wait before saying not found. When I try to ping G41L5420, the response is an immediate no. Kinda suspicious...

Dell is the NetBIOS Master Browser on the network. That computer is the most online nowadays in the house.

It seems it was a firewall related issue, that's why the immediate errors without timeout.

I ran the troubleshooter from settings/updates/troubleshooting/incoming connections (bad translation from Hungarian) and selected troubleshooter for file- and network sharing.
It solved it, though after putting the old computer name back, I needed to rerun the troubleshooter.