I am sure that happened to us. I had booked quite a few but when I checked via the site, several were missing. However, I had e-mailed the list to myself straight after making them and the ADR’s were on that list. I printed it off and just thought well I’ll just show this if theres a problem.
Keep trying, it may be the site, but if not give them a call. I had tried making one or two again when it happened to us, and when I got to Sci Fi diner there were two reservations in my name, so they are there just not visible!