Thanks @David-TP for writing.

i) About my question about the double ARP query from the main Deco X20, I'm still wondering if it's normal behavior.

ii) About Deco reboots, I made two changes to my network and the reboots are gone, at least, for now... 2 days no reboots.

One of the changes I made was to the physical network connection of decos. I wrote that all Decos connect to the TP-Link LS1008G giga switch in a star topology. However, only one of the M4 deco was connected to the second port of the non-main X20 deco. So now, using one fiber optic and two Gigabit fiber optic media converters, I connected that M4 deco directly to the TP-Link LS1008G. So now I have a true star network topology.

The other change was that I turned off my Raspberry pi 4 (rpi4). I have on it: Docker+Home Assistant+Duplicati+Plex Server.

So maybe, just maybe, one of those programs could be causing a problem. For example, Duplicati is backup software and when it runs it means a LOT of traffic within my network between the rpi4, the NAS and my internet connection uploading the backup to Google Drive. Could all this heavy traffic trigger reboots on the main Deco X20?

Or... Maybe Home Assistant is sending some kind of network traffic that could affect the main X20. Or maybe Docker has its own network services that are reaching the network somehow and causing the router to reboot. Same with the Plex server. etc.

So let's keep my network as it is today for a few more days. If everything works fine, I'm going to turn on the rpi4. If the network is still good with the rpi4 on, the conclusion was that connecting an additional deco to a second port of a deco was no good. If the problem comes up again, I'll investigate the different software inside the rpi4 to identify who is the bad guy :S

I will inform the community when I have any conclusion.

Thanks again,

Fernando.

Quick update.

Unfortunately, after much testing and much analysis with Wireshark, the main Deco X20 keeps rebooting randomly.

I must say that since I connected a remote M4 Deco directly to the tp-link switch that was daisychained to the second port of an X20 (not main), it has worked better, i.e. less random reboots. But we went from 2 or 3 reboots a day to 1 a week.

I'll keep doing tests, including the test of taking the 2 Decos X20 (v2.0) off the network and putting everything back as it was before with 3 Decos M4, but I'm ending this thread. In case of any news I will open another.

Thank you all,

Fernando.