Booking.com has resolved the incident on their side.

Booking.com's incident remains ongoing, with reservation delays of 10 to 30 minutes. We will update when this is resolved.

Here's the link to their incident page: https://connect.booking.com/status/incident/477

Booking.com has an ongoing incident with reservation delays; thus, we have a delay in receiving reservation information too. More information here:

https://connect.booking.com/status/incident/477