If a network share no longer works due to update KB4480970, the best way to fix this would be to run an elevated command prompt and paste the registry entry below.
reg add HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\system /v LocalAccountTokenFilterPolicy /t REG_DWORD /d 1 /f
Restart PC after fix and the PC having trouble accessing the share should then work. The PC requesting the share should not need to be restarted.