Thanks. Actually, this is crazy, I think I have "solved" the issue. I will list it in the next post.

@David-TP it has happened again and there is even more bizarre behaviour. This time the exact same device (3D printer on 5GHz network) could be accessed by any device on local network - ethernet,...

@David-TP I have the exact same issue. I have two Deco XE75 Pro working as access points. I also use Pihole as DNS server and ER605 as main router. Main Deco has same error messages for NTP, same...

@David-TP I cannot ping the Pi 4 from any 5 GHz device. As this used to happen with WDR3600 and now with Deco XE75 Pro, this is something to consider in the investigation. They are both TP-Link...

I have a strange problem and I am not sure it is isolated to Deco XE75 Pro, it could also be related to Omada ER605. I have Omada ER605 router set up as the main router and DHCP server. I have two...

@Clive_A Thank you for replying. I am still confused after reading those articles. I have one wireless router for all of my wireless devices. That router is not a DHCP server, it only acts as an...