How do you know it isn't the "repeater"?
If it connects fine with your cell hotspot, but not the repeater, it kind of sounds like its the repeater!
SO, does your machine browse on a wired connection for any length of time? If it does, then the machine is good!
If it only has issues with WIFI, perhaps the CHANNEL it is broadcasting on is conflicting with another close range WIFI device? Change the channel it is broadcasting on.
Do you have the repeater as the same password as the main WIFI? How close are the two devices to each other? Is your device seeing one WIFI, then seeing the "repeater" and trying to "switch" to it, causing a lag, then seeing the other main device, and switching to it, causing lag? It WILL happen!