Yiiiiikesss, i have same problem in the past. I left the skimmer running for about 1 1/2 month without cleaning and thats what exactly happen to my beckett skimmer. Algea getting stuck in the injector nozzle is not a cool thing. So, i've learn that i need to clean it at least once week.
That was some macro algea from my refugium that I feed to the tangs. It had gotten loose from the lettuce clip and made it's way to the skimmer intake is my best guess. Luck I didn't burn up the pump. But boy is the skimmer working overtime now. Back in business.