@Itay_a 

Thanks for reaching out. I understand that you have a Deco Mesh network where your two wired Deco M4R units are frequently disconnecting (showing a red light), while the rest of your Deco units remain stable. You mentioned that this issue started recently after a firmware upgrade, and the network was previously stable for several years.

Based on your description, here are some troubleshooting steps you can try to resolve the issue:

1. Check for Continuous Reboots or Boot Issues
• If the affected Deco units are stuck on a solid yellow light during startup, this indicates they are stuck in the boot process. In this case, please attempt a firmware recovery by following the instructions in this FAQ: https://www.tp-link.com/support/faq/2958/
• If the Deco units are turning on and off repeatedly (cycling through yellow, green/red/blue, and back to yellow), try the following:
    1) Use a different power adapter or power outlet for the Deco unit to rule out power supply issues.
    2) Disconnect all Ethernet cables and client devices from the Deco, then observe if the issue persists. This can help identify if a connected device or cable is causing the problem.

2. Additional Suggestions
• Since you suspect the issue may be related to the latest firmware update, you may want to check if a newer firmware version is available or consider rolling back to a previous version if possible.
• If the problem only affects the M4R units and not the X20 units, it could be a compatibility or firmware issue specific to the M4R model.

If the above steps do not resolve the issue, please contact TP-Link support and provide details of the troubleshooting steps you have already tried.

Note: If your Deco units are still under warranty, TP-Link support can assist further with advanced troubleshooting or replacement options if necessary.

@Itay_a Try updating your X20s