Hello community. I live in an apartment and I have a 1200mbps plan with my ISP. I set up this wifi extender inside the same room as my ISP Modem/Router. When i connect to the ISP router via my iphone 15, i get anywhere between 400-600 mbps.

When i connect to the extender, I get about 120mbps. What gives?? 
 

Originally, i had the extender located in the living room, and i was getting about 120mbps there, too. Something is not working right if the extender is giving me these slow speeds, whether it's plugged into the living room or into the same room as the ISP router. 
 

This is all using the 5ghz band. I even tried experiments with the 2.4ghz band disabled on the extender. Same results. 
 

i had these poor results out of the box, and even after updating the fw, the results are the same. 
 

Hight-Speed mode is on Auto.

Location assistant says Strong Signal.

Wifi Coverage is set to Maximum Coverage.
 

why is this AC1900 wifi extender working so poorly??