Hi,

Theoretically, the extender won't affect the performance of the main router; Do they use the same network name now? Please give me the below details so that we can do more troubleshooting.

a. What's the light status of the 850RE and main router when the extender stops working? Please tell me the model number of the main router/modem as well.

b. How often it drops connection, and can you see the extender's wifi at that time? Try to login to the web page of the 850RE when the connection lost and take a picture of the status page.

c. Please connect your computer to the 850RE directly when the connections drop out. And please check the IP address, default gateway and DNS server as the below instruction.
https://www.tp-link.com/support/faq/838/
Note: Please show me the screenshot of the status-details page.

d. At that time, please connect your computer to the main router directly and test the IP, default gateway and DNS too.
Note: Please show me the screenshot of the status-details page.

e. How far away between the extender and main router And what's the wifi signal strength?

Thanks in advance, and have a good day.