Hi My devices recently have started to disconnect very frequently on 2.4 GHz band

I have already tried the following

1) Resetting the BE400 (AP) to factory reset

2) changing the channel

3) Enabling 20 MHz, 40 MHz, 20/40 MHz

4) Enabling IoT 

5) Separating the Smart Connect

All options have failed, when I connect to 2.4 GHz band on laptop or mobile the speed varies from 0.2 MBps to 8 MBps while my 5GHZ provides speed of 250 MBps

Need urgent help on this, anyone was able to fix this or this access point is faulty?

Note: I am using BE400 as Accesspoint and not in router mode.