The pi3 has trouble with the higher wifi channels, mine would see my router on channel 11, but was transfering at under 12kbs a sec.
Changing the wifi channel to an open lower channel worked for me.
(To see what channels are in use, the easiest way I’ve found is use the free wifi-analyzer app on an android device. It shows you all the wifi signals it sees in a nice display so you can see where the channels are congested and move yours to an open one.)
Later,
dabone