Zapier users with Zaps connected to some Facebook functions (Facebook Pages, Lead Ads, and Offline Conversions) may be experiencing timeouts (500-code errors). This may cause your Zaps to temporarily be delayed, or not run. These requests can/will be retried later after the outage is passed.
Facebook has identified this issue and is currently working on a resolution. You can follow updates directly from Facebook's developer site here: https://developers.facebook.com/status/issues/