@David-TP 

I have reset the RE450 and it's still the same all lights are blue and 5GHz is available on WiFi but just doesn't connect. Firmware is to the latest. The router is only one band connecting it's just my booster that has the 2.4 and 5. I just don't know why it worked for so long and one day just stopped. I will look into changing the channel and see if that helps, thank you.

Sometimes, a simple reboot can resolve connectivity issues. Unplug the range extender, wait for about 10 seconds, and then plug it back in. Allow it a minute or two to fully restart.Ensure that your range extender has the latest firmware installed. Visit the TP-Link website, enter your device model, and download the latest firmware. Follow the manufacturer's instructions to update the firmware. If a reboot doesn't work, consider resetting the range extender to its factory settings. There is usually a small reset button that you can press and hold for about 10 seconds. After resetting, reconfigure the range extender and see if the issue persists. Confirm that the 5GHz Wi-Fi settings (such as SSID and password) on the range extender match those of your main router. You may want to log in to the range extender's web interface to verify and adjust these settings.