I don't have any Sonoff devices at hand to answer this conclusively, but I think it has to do with the settings. According to my brief research, Sonoff devices use 802.11 b/g/n which are quite old standards (the former two in the 2.4GHz band). Modern routers have switched off older WLAN standards for security reasons but also for better performance. I have the same problem e.g. with my Garmin GPS with which I cannot connect via WLAN to the new WLAN AP optimised for speed - but it works on the WAP3205.
The WAP3205 series also supports the 802.11 b/g/n standards, so I assume that it will work without any problems.