Hardware V1.20 (i was unable to pick V1.20 on the hardware version)

Today i had an issue where my Archer AX20 suddenly was not able to give a good wifi signal. 

I had not changed any thing for the past few months where the location and coverage was perfect until today.

Suddenly i was not able to get the wifi signal from the AX20 via its 2.4ghz band. Although the 5Ghz was accessible but it was still weaker than normal. 

Now, i am not able to connect to the router via the 2.4ghz unless I am literally beside it. Infact the 5ghz band has a better range than the 2.4ghz band, althought both still showing weaker wifi signal than normal.

Setup is that i have 1 primary modem/router provided by my ISP. My Archer Ax20 acts as an independent router connected via LAN from the primary router from my ISP into the AX20's WAN port. 

Signal from the  primary modem/router seems to be normal but that being said, doesnt cover the household hence why i got the AX20. But now the AX20 is alot worse than the primary modem/router i have.

I have tried to:

1. Restart AX20 Router and Primary Router/Modem

2. Factory Reset.

3. Firmware is up to date.

4. Tried restoring to an old firmware also did not fix the issue. 

Please advise what i should do or try.