In an AP group we have five R750, one R550 and two R710 access points.
ZD 1200 with latest firmware is the controller.
All are connected with Ruckus 2.5 G supported POE+ switch
Internet connection is of 100 Mbps CIR
Surprisingly, when connected on 2.4GHz, the mobile devices works well with R710 only.
On all six R750 and R550, any Mobile new or old, doesn't get the speed above 10 Mb. Most of the times it remains even less than 1 Mb.
Speed on LAN is ok.
Please share if tweaking required particularly for new models.
On which FW are you (both on mobile devices and ZD)? It sounds to me that your devices don‘t like the wifi-ax which the newer APs speak. I remember that this was pretty common and you should keep firmware and device driver up to date.
As an alternative disable ax for testing purposes in the ZD?
Firmware of ZD1200 is: Version:10.5.1.0 build 176
Wi-Fi Device on which I am testing is Samsung Galaxy S21 Ultra, it works perfectly with other APs. There are plenty of other users with latest mobile phones with same complain
Let me disable WiFi-6 on 2.4Ghz SSID and see as you suggested