The grid needs to be balanced, i.e. the supply and demand must match. You can't pump more power than needed just because you can, otherwise everything stops working.

Given this, it's possible the reason is that there wasn't enough demand at that time, especially if other wind farms were generating enough power given the strong winds.

Not an expert by any means, just an educated guess.

Was it really windy? Turbines need steady medium wind speeds to operate; when the wind speed increases above a threshold they stop generating, and sometimes angle the blades to reduce the drag (so the mast and foundation aren't overstressed).

I can't say for certain but some experience in the electric grid space gives me some of the following reasons:

The circuit they are connected to was faulted

They were transferred to a supply that they are not approved to generate on

If they are a large facility then they might have had a failed communication channel that is used to disconnect them if there's an issue.

This isn't an exhaustive list but just some common ones

Saving the birds? (/s)