Suddenly wifi speeds on x90 is very slow.

I subscribed to a 1gbps fibre plan.

I tested..

modem direct lan connection is 945mbps/ 900mbs via Speedtest ookla

router Lan connection is 900mbps/ 900mbs ookla

but wifi is 60mbps/ 200mbs using deco lab wifi assistant via mobile phone

wifi 60mbps/ 50mbps on laptop via Speedtest ookla 

previously everything was fine. I was getting wifi speed of 450mbps/ 120mps 

I spoke to my isp, they said that everything on their end is fine.. ask me to check with tp link..

is there a way to fix it?