@Vk2020 

Good day.

You could try some tips in below thread and change router 5Ghz channel to 36/40/44/48 :
[Troubleshooting] TP-Link Range Extender is not detecting the 5GHz Signal of the Main Router

Could you please help us check the following information：

1. May I know the hardware and firmware version about the RE305?
2. What is the model number of your main router?
3. If it could not detect the main router’s 5ghz, how about other 5ghz networks around?

If possible, please try to Change the wireless advanced settings for the 5ghz, like channel 48 and channel width 40mhz for 5ghz;

Thank you~