Hi! Recently I changed my ISP brand router by the Linksys wrt1900ac. It works well with every devices on my home, except my Galaxy Note 4, that conexion drops when I download a large file, and performance too bad. It seems like a incompatibility between the BCM4358 (used on both Galaxy S6 and Note 4) and the Marvell chipset of the wrt1900ac (mine is V1).
It happends on both bands (2,4 and 5 Ghz)
I test everything, I changed Wifi channel on 2,4 and 5 Ghz, changed Wifi bandwidth, i disabled 5Ghz band, I disabled wpa security, I put last OpenWRT firmware, and last Official Linksys firmware...
The only solution I find is disable N-Band on 2,4 Ghz... (and get a crappy speed 
)
When I connect my ISP router (zyxel p8701p) it works fine with note 4.
Samsung SAT told me that is a router issue, the phone is fine...