Do a wireshark and find the error.
The only scan setting that would have changed is you would originally not been able to support SMB2-3 and been using port 139.
The newer firmware does support SMB2-3 and uses 445, it does not in any way contain Windows Networking (NETbios/TCP/IP) so scans on port 139 fail. In turn, this would then add that time needs to be within 3 minutes and Windows 8 and up would need a different username format than the older firmware. Which is easily found server/PC side (you need the name as it appears in the brackets exactly)
But the Wireshark will be enough to show you that. The protocols will apear different between the devices on different firmwares.