Happened to me (on .App and .Com) late April after 13 nights with 5 remaining.
Hotel front-desk said there was an update to Opera system over the weekend. Ok, but reservation did not re-appear. Made sure Folio received by email PDF before leaving the property.
Emailed to Consumer Affairs before checkout. No reply.
Stay posted normally
Another issue: made bookings at two properties 15 minutes apart ...one property: no email confirmation and did not appear on .Com or .App until 24-36h later.
When email confirm did not arrive in 10 minutes, screenshot the webpage of booking with confirm# and emailed Consumer Affairs.