Coronavirus (COVID-19) has a global impact on Overall Economy. According to Facebook Official post; they are working with partners to send home all contract workers who perform content and ad review, until further notice.
To minimize business disruptions; Facebook will remain committed to keeping their platform safe. The ad might be reviewed with a delay; and you can also expect reduced or slow response time on appeals. When the new ad is created it goes through a review process. Also any significant change in existing ad will trigger the review option.
What are best practices to Prevent Delay?
To avoid review trigger; only change the start/end date or budget of an existing ad.
Avoid making changes in your ad if they are performing well