Getting less coverage for the router.

Hi,
I am facing an issue on my wireless router modem. I am using the DSL internet plan. The modem is Smart RG SR505n https://www.acanac.com/hardware/smar...?package=fibre , it has a build in router. the problem is the coverage of the router has declined within \a single room. The modem router is in the hall. I used to get the internet from the lawn and farthest room. But now, I am not getting the signals beyond the hall kitchen. What might be causing this? There are no fluctuations in the internet speed when I am within the range, i.e., the hall.
Please help me identify the issue and resolve it.

Thanks.

Usually for me, in the past that was caused by a brown out , voltage drop in the incoming power, to fix that mess, I reach behind and pulled the power plug, wait 30 seconds, and plug the power back in. When back up, test it.

My modems and routers are now on a uninterruptible power supply [UPS].
https://en.wikipedia.org/wiki/Uninte...e_power_supply