Suddenly, constant UDLD alerts

[EJN]

The only thing that happened is a Netgear switch downstream came back online after a power outage.

The alerts are getting generated on many/most/all of my uplink ports on multiple Meraki switches.

I'm new to UDLD.

Where can I start troubleshooting? Most common causes for this?

[alemabrahao]

Take a look at this article:

https://documentation.meraki.com/MS/Other_Topics/Unidirectional_Link_Detection_(UDLD)

[PhilipDAth]

I would try:

* Temporarily removing the cable to the NetGear and then plugging it in.

* Power cycle the NetGear.

The problem is most likely transient.  There is a slim chance it is the cable, or you have a damaged switch port.