Sometimes services on IFTTT run into issues like high error rates. To prevent Applets from being disconnected, services are paused automatically or by someone on the IFTTT team when an anomaly is detected. This could be a reason why your Applet did not run.
A paused service does not perform trigger checks, so the Applets don't run the actions. The "Check Now" button is also disabled.
As soon as the service is unpaused, the Applets will continue to work as expected.
Whether or not the Applets will pick up missed events when a service is unpaused depends on the nature of the underlying issue and the service itself.
Visit the status page to check out which services are currently paused and subscribe for updates.