Does condensate on a skylight indicate a broken seal?
It's possible that your double pane glass has failed.  You should examine it closely under less extreme conditions.  If the interior has a "fog" in normal conditions, then the gas has likely leaked out.  Sealed window assemblies are only warranted for about 10 years.  Some last longer than that.  YMMV

I replaced all my Velux window panes a few years ago, when I was getting the roof redone.  They were fogged and had interior condensation frequently in the winter.  I contacted the manufacturer, and was able to special order replacements via the local Home Depot.  Though it can depend on if the model is still in production.