I am using a RB750Gr3. I have it connected to the LAN ports of WiFi routers with DHCP turned off to use them as APs.

I am able to get internet on my phones and Ubuntu laptops. However, my windows and mac laptop cannot seem to get full Internet access anymore. It detects the wireless network, connects to it, and has decent signal strength. I can even ping 1.1.1.1 and the router address (192.168.88.1) as soon as I connect. However, after one or two pings it starts timing out. If I plug the laptop into the router directly—and thus not using the wireless connection—it works fine.

This happens on multiple windows and mac devices simultaneously so I ruled out driver issues. I can ping all the devices on the network except the router itself. I can even ping the routers connected to different ports on the RB750Gr3.

Since this is a very windows and osx specific issue, I don't have any guesses.

It turns out that someone in my network was using an application called netcut that was causing the issue.

I do suggest you put some restrictions in place to disallow the use of such applications to avoid a re-occurrence.