Signal received a sudden and unprecedented rush of traffic, and things started going wrong pretty quickly. Messages either took a long time to send or didn't make it through at all, and Signal issued a statement to say it had been "adding new servers and extra capacity at a record pace every single day this week nonstop, but today exceeded even our most optimistic projections."
Signal's sudden rise could have something to do with the fact false rumors have been spreading in recent times concerning WhatsApp - which also features end-to-end encryption. Whispers circulating said that WhatsApp would soon start sharing messages with with Facebook, but the stories were untrue. The change only relates to instances where users use the app to talk to businesses via the app's customer service function.
Signal was founded back in 2013 by Matthew Rosenfield, who uses the pseudonym Moxie Marlinspike. The app has been used by privacy-seeking journalists and activists for years, but the demise of Trump and the fallout connected with that has seen the app's popularity rocket. Law enforcement doesn't exactly love Signal's end-to-end encryption, and that's mainly because extremist groups, criminals, and terrorists can use it so send encrypted messaging totally undetected and without risk of prosecution - and it looks like many of the Trump-supporting far-right extremists have left the more mainstream social apps and taken to Signal in droves to take full advantage of that privacy.