I had the same problem of finding "sold out" tickets for the first three to four minutes, but I was searching for the "best available", so presumably would have been hitting the most expensive seats (ie, it wasn't just the cheaper seats that were unavailable). There did appear to be something up with the system, as I would receive the "Sorry, no exact matches were found" message almost instantly after entering the captcha text, with no pause for the searching screen.
Then, on my fifth attempt to get through I was kept on the "searching" screen for about three and a half minutes (all the while it said "your wait time is less than one minute", and when it finally went through the "best available" (lower reserved seating) were two full sections back from the stage. I released those tickets and tried several more times over the next fifteen minutes but never hit on anything better. All of those searches went through in under 20 seconds, for whatever that's worth.
I'll try again on Tuesday when the general onsale starts. Hopefully I'll get luckier then

(Obviously some people were getting through in those first few minutes when we were being blocked. It would be nice to know if any actual fans were lucky enough to get seats in the close (non floors) sections, or if it was just the resellers

)