@MoustafaDida 

Hello，

For this issue, we need to check the issue that happened on the router or range extender.

Please try to use the RE300 separately, do not use the Onemesh function, then check if the RE300 has a stable connection.

Please reset the RE300 and set a different network name when you reconfigure it.

If RE300 still has an unstable issue, here are some suggestions you can try:

For the RE dropping-out issue, please refer to this FAQ to troubleshoot at first:https://www.tp-link.com/en/support/faq/2233/

If still the same issue, can you help us confirm some information:

1. Please let us know the troubleshooting steps you have tried in detail, thank you!

2. How often this issue happens? What about the LED Status on RE when this issue happens?

3. May I know the problem occurs on 2.4G or 5G wifi?  How long do you have this RE and when did the issue start?

4. Did you put RE in very close to router (within)and check stability?
 Do you have a stable WIFi connection from the main router? 

6. If the RE Led is ON when the issue happens, please send us a photo of the IP address on computer:
https://www.tp-link.com/en/support/faq/838/

Thank you for your precious time.