On Monday, Reddit’s ad manager encountered a brief outage, during which buyers were unable to look at reporting statistics, even while impressions were still delivering, though the impact was fairly minimal, per four sources. (The Verge reported the moderator blackout crashed the site, although it’s unclear whether the crashes are related).

So the site was down for quite a bit of time but the ad related stuff was just a minor hiccup?

It's not possible https://github.com/LemmyNet/lemmy/issues/1985

The other issue linked at the end says the possible solution is to export/import some data, like subscriptions. But it's not implemented yet.