Had a small client's IT request our help with some loop issues in their network.

Loop protection was on and was triggering, but they could not understand what was causing the loop.

After poking around saw that loop protection was triggering on ports with Ubiquity APs connected to them. I was like "Huh, that can't be right..." After some more pocking around nothing else seemed be the culprit so decided to check the Ubiquity AP config. Turn out mesh functionality was on and the AP decided to make a mesh network out of the blue (never happened before).

Turning mesh off solved the problem. Albeit some AP refused to turn it off and had to be reset.

EDIT: Just to clarify the purpose of sharing this anecdote, which is two fold:

1. The fact that APs can cause loops through meshing was just a surprise to me - makes sense, but never thought of it. Figured someone would benefit from this tidbit or be reminded of it.

2. Ubiquity APs refused to turn off meshing. Which just re-affirms the bad rep they have.

Yes, the APs were misconfigured - that much is clear. The issue - surprisingly - did not rear its head for a few years.