Edit: This problem has disappeared. It works as expected now.
Edit 2018-12-10: Right now the problem has returned.
My question filter is supposed to show all questions from Travel, Academia, Outdoors, Earth Science, and a number of other sites, as well as a selection of tags on Physics, Astronomy, and others. However, currently it only shows the selection of tags, but not any questions from the sites where I want to see all questions. The screenshot below only shows questions from Physics, Astronomy, and Bicycles. I know the other sites, where I want to see all questions, have had questions in the same period. But they're not shown.