Rebooting of Nighthawk MR5100, wifi signal strength loss, alternating between 4G and 5G

I have a few issues with my Nighthawk MR5100.

Where I placed my wifi in my room, after I bought it, a month ago, it showed 5 bars with excellent signal strength at 5G and fast download speeds. It never went to 4G in that location.

A week ago, a month later,  all of a sudden the mobile router's signal strength in that same location went to 4G, with slower download speed and the signal strength varies between poor to fair.

I found a location in my room where the router is at 5G but the signal strength varies from fair to good, but not excellent, not like how it used to be for one month. It can also alternate between 5G to 4G in that location.

A few times the router has rebooted itself.

The temperature in my room has not been too hot and the router doesn't feel too hot.

I use the 5GHz setting.

I have rebooted the router daily and even reset the router to factory settings quite a few times.

Any ideas?