If the Windows systems are using the same HP Probook G series without issue, then you can basically rule out hardware - so the laptop and the Meraki access points. So it comes down to the configuration and the drivers. I would start by looking at the drivers for the WiFi on the Ubuntu systems and see if there are updates available there, then see if you can spot any configuration differences between the Ubuntu systems and the Mac (since as they are both Linux variants).
@luanvh check the wireless chipsets in the Ubuntu laptops, if they are Intel WiF5 chipsets (826x, 926x) then see if they are okay when plugged into the power. If they are then check for power saving settings in the wireless drivers and disable Mu-MIMO /SIMD power saving first, then all power savings if that doesn't work. There seems to be an issue when those kick in that causes packet loss, performance drops and then effective disconnection.
Hi @cmr , I tried disabling wireless power management (wifi.powersave) and disabling IPv6 on Ubuntu OS, but it didn't solve the problem. Also,I can't disable Mu-MIMO, I don't think Mu-MIMO should be turned off because it's a technology that greatly improves WiFi reliability.