@Harshita Hello,
May I know the model of your RE and please confirm its firmware is up to date.
May I know the model of your router and how about the Wi-Fi LED on RE when issue occurs?
> Try to turn off Advanced WiFi settings router like : Band Steering or Smart Connect; WiFi optimizing etc.
> If the WiFi Led(s) goes off when issue occurs, please locate RE closer to router and change a different WiFi channel of 2.4Ghz / 5Ghz on router and see if that helps with the issue.
> If RE LEDs look normal when issue happen, please log in to Range extender's web page , turn on RE's DHCP and set up a static IP address for RE as FAQ below and see if that help with unstable issue: https://www.tp-link.com/support/faq/2965/
Also make sure you have a stable Wi-Fi connection from the main router at RE's location.
If the issue persist, may I know does the issue particularly happens on RE's 2.4Ghz and 5Ghz, and how about your network topology, thank you.