First, I would look at the data to see if there are any obvious patterns. I would check if the drop in RSVPs was specific to a particular type of event, location, or time period. If I notice any correlations or trends, I would investigate further to see if there was a specific issue affecting those events. If I can't find any obvious patterns, I would reach out to the team responsible for the Facebook Events product to see if they have any insights. I would ask them if they had made any recent changes to the product that could have impacted RSVPs. Next, I would reach out to a small group of users who had recently RSVP'd to an event to get their feedback. I would ask them if they experienced any issues or had any feedback on the RSVP process. This feedback could help identify any potential issues with the product. Finally, I would consider running some A/B tests to see if any changes to the product could help improve RSVP rates. I would work with the product team to identify potential changes, and then test those changes on a small subset of users to see if they improve RSVP rates. Overall, my goal would be to quickly identify the cause of the drop in RSVPs and work with the team to develop a solution to improve RSVP rates going forward.