Interesting - I have the same router and it connects to the 5GHz without issue (I have a Surface 3, 3x SP3s and 1x SP4 all connected to the R7000).Yes separate SSID (one with 24G suffix and other one with 5G suffix)
My router is Netgear R7000
Last firmware
WPA2-personnal for security
2.4 Ghz => N Only
5 Ghz => N/AC mixed