Hello @Toovijju 

Please check the Led status on RE, if the circle of signal LEDs goes off, range extender might have disconnected from wifi, you could try to factory reset the range extender and reinstall it as guide here 

• Single-band RE:  How to configure my 11n Range Extender via Web GUI  (new logo)

You could also locate the RE closer to wifi router, change a different 2.4Ghz wifi channel on the main router and monitor the performace(scan wifi channel using app like wifi anlyzer app and select a less crowded wifi channel on main router,usually channel 1,6,11 are recommended on 2.4Ghz wifi. )

Here is a related thread:  How to place your wireless Range Extender for optimal reception and performance?