Hello   @TechEditor1 

It's good to know you have tried some tips in troubleshooting guide here 
[Troubleshooting] TP-Link Range Extender is not detecting the 5GHz Signal of the Main Router

Most of the time range extender not see router's 5Ghz is due to router's 5Ghz channel as explained in the above guide, in some other cases it could be a faulty extender or something else, and there is no existing known issue for this model 5Ghz. 

May I know is the issue that range extender not see router's 5Ghz Wi-Fi signal during set up? Can range extender see other 5Ghz signals in the neighborhood? 

1. Please share a photo of RE scanning for 5Ghz SSID page

2. model of router

3.  a photo of router 5Ghz settings

May I know when did you purchase the extender, did the extender work with 5Ghz Wi-Fi before? Thank you.

If you have a different router or AP, you could also test if extender could see 5Ghz of a different router/AP. If you have tested another AP, and range extender not see any 5Ghz, you could reach the local retailer or local support to get a replacement first. 

For the urgent help, you could also call our hotline call our hotline or reach chat support, so they can assist directly.