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.