Dataset totally stuck, cannot refresh

I have a dataset in the Power BI Service. Its data source is Amazon Redshift. It normally takes 10-15 minutes to refresh, which it does every few hours.

Yesterday, one refresh got "stuck." It spent several hours where in the "Refresh history" screen it said "In progress;" but on the Datasets screen in the workspace I had the yellow triangle "failure" icon (not the spinning "in progress" icon). It seemed stuck.

After some more time, it seemed to get un-stuck, and in the "Refresh history" screen it displayed this error message:

The refresh operation failed because it took more than 120 minutes to complete. Consider reducing the size of your dataset or breaking it up into smaller datasets.

But now, I cannot refresh the dataset, or anyting. It really is stuck!

Clicking "Refresh now" does nothing. (Well, for a second in the top-right corner, the "Preparing for refresh" message appears, but then nothing happens.)

A scheduled refresh does nothing. (And I don't get an email notification of an error; just...nothing happens.)

I have tried re-publishing the dataset from Power BI Desktop, to overwrite the dataset in the Service…and in Desktop I get a "Success" message...but it does not actually do anything in the service. The old "stuck" version of the dataset persists in the Service.

Any ideas? (I've opened a ticket with Microsoft support, but no help so far, and it's quite urgent!)