The second paragraph I will need help with also I'm not using SMB but NFS and it detects the IP address.sorry I mised that, yes so looks like probably a network related issue , i would try with rebooting all network related devices in the chain , and powering off/on any switchs/hubs etc.
I would also set the U22 to DHCP and assign its IP with dhcp reservation on the router.
Also in Kodi add the source (NAS) via its IP address ( Add netwok location ) rather than through workgroup. ( Windows network (SMB))