Ntoskrnl.exe--is the file used for file and print sharing..
So all the computers in the network poll on the UDP port 137 ,138 to find computers near them.
So even if you are not using the remote computer for file sharing you might get this pop-up.
Since on Unmanaged computer the option for Browse File and Print sharing on the Network in unchecked ( turned off )
So you might be getting this pop-up.
So what you can do is
Open SEP Interface-Under Network Threat Protection -Options-Change Settings-Microsoft Windows Networking-All network Adapters--Check both the boxes below then one by select all the adapters and make sure both the boxes are checked for all you Network adapters in the drop-down..