"I think the
@signalapp
apps DDoS'ed the server. Servers ran over capacity due to influx of users and started to return HTTP 508 which was not handled by the app and millions of apps started retrying the connection at once. Judging from recent commits in https://github.com/signalapp/Signal-Android/commits/master" https://twitter.com/NovakDaniel/status/1350471722034745348

Easy failure mode to overlook.