Hello @user966886 ,
It looks like this is something our engineers have seen come up before, and are investigating the cause of. I've submitted your case to the engineers, with the relevant service request attached. If and when they have an update for you, they'll make sure to reach out.
To aid their troubleshooting, did you attempt to disconnect or reconnect your Facebook account to the Lead Ads Manager at any point, while the ad was running?