Good morning everyone.
I have a Rb2011 uias with RouterOs 7.9.2 on board
The routerboard has been running for several weeks, never showing any problems.
An unmanaged switch (to which several PCs and other network devices are connected) is connected to the ether6 port.
Since this afternoon, all devices have stopped browsing.
Entering the mikrotik log I read a series of warnings: bridge rx looped packet ethertype 0x0004 and ethertype 0x88cc
No network ports have apparently been moved so I doubt it could be a network loop (but I can't rule it out for sure).
I rebooted the routerboard and it worked for about an hour, then stuck again with a series of bridge rx looped packet ethertype 0x0004 and ethertype 0x88cc messages.
I have shut down all the PCs and devices, but still it continues to give me this problem.
Tomorrow morning I will personally go to the site to better investigate the problem. What could it be? Can I do something remotely to try to resolve?
Thank you all

For clarification:
Last Friday I installed some Cisco SPA ip phones connected to this switch. When I finished the setup all the devices were working fine.

Those are LLDP packets, presumably whatever device 4c5e is, is broadcasting LLDP packets, they go out ether6 and there's a loop at the unmanaged switch and the packet comes back. Perhaps some user connected the passthrough port of the IP phone to the switch. Either way you probably have a broadcast storm going on if you check interface traffic levels / torch.

Those are LLDP packets, presumably whatever device 4c5e is, is broadcasting LLDP packets, they go out ether6 and there's a loop at the unmanaged switch and the packet comes back. Perhaps some user connected the passthrough port of the IP phone to the switch. Either way you probably have a broadcast storm going on if you check interface traffic levels / torch.

Hi R1CH. Thank you for your answer.
At the moment I solved, with a very strange solution.
I checked visually and the ether6 port is unplugged (!!) there is no ethernet cable connected. I tried to connect my PC to ether6 and it doesn't work. The green LED on the routerboard doesn't even light up. At that point I removed the ether6 from the bridge and disabled the interface.
Everything is distributed perfectly (the unmanaged switch is connected to the ether7)
Absurd.
I don't understand if it's a failure (what a strange failure) or something more

Device 4c:5e.... is the MAC address of the ether6.

Odd, sounds like some kind of weird hardware failure in that case.

i think that kind of warning appears when Router/Switch receives a Frame with a Source MAC Address belong to it