In the menu on the left side of the screen, I clicked on settings, which brought me to the settings screen. In the settings screen there are options for which nodes to connect to. There is a dropdown list for Avalon nodes (Avalon is the blockchain that Dtube runs on), there is a dropdown list for Steem nodes, one for Hive nodes, and one for Blurt nodes. I think that the default node for Avalon wasn't working, so switching to a different one fixed the problem. If you're on a mobile device, you might have to click on the hamburger button (it's the square that has three lines in it) to access the menu.