@TanzeelShedde 

I do not think it was the extender that caused your issue.

Did you change any settings in the router at that time?

I would try the following:

• Be sure your firmware is up to date.

• Ensure you are using the power adapter that came with the router.
• Be sure the Ethernet cables are at least CAT 5E or better and in good condition.
• Power cycle all (Power off modem, router and the PC, power up the modem, wait for it to stabilize, then power up the router, wait for it to stabilize, the power up the PC).
• I would turn on IPv6 if it is not on already
• Check to see is all of the antennas are attached correctly.
• Reposition the router if you moved it as other devices close to it can affect it.
• Be sure to use a different SSID on the extender than the main router.
• Do a factory reset on the router (note that you will need to reenter all your router settings)
• On your devices that have the connection issues to WIFi, delete (forget) the networks on them and re-establish them.
• Use different WIFI channels and widths

The more I think about it, I sort of suspect that you used the same SSID on the extender as the router.