You might have a dead zone with no Wi-Fi between your router and extender, or you might have clients that don't like to roam, or you might have interference.

You can sometimes fix a dead zone by moving equipment around, but if you want a fast network everywhere then you'll probably have to add more extenders. Most clients can connect to two extenders at once, so adding another extender in between can make the network much more robust.

For Intel chipsets in Windows you can set the "roaming aggressiveness" in the advanced settings for the adapter, see:
http://www.intel.com/content/www/us/en/support/network-and-i-o/wireless-networking/000005585.html

For interference you can try using channels 1 and 11. The wpa4220 should extend either one to a 40mhz channel and you'll get a great connection.

You can also download a scanner like https://www.netspotapp.com/ to see what channels other people are using so you can avoid them. The Wi-Fi channels overlap so there is a bit of a mess.