I had a similar experience. I got assigned number 300-something in the beginning, but when it was time for me to get to the front of the line, it hiccuped and then kicked me out. Then when I got back into line, I was number 1500-something, which was not so bad. It hiccuped again when I got to the front, but then let me in around 10:23 and there were plenty of seats available.
So I think that means that only 1500 people (plus potentially some unknown number that were let in without a queue number at all) wanted to buy tickets this morning.
The email said that we would be able to pick the seat, but that was not the case. I was only given one choice at a time, at least on my phone. Did you get to pick your seat from a map? But the choices were plentiful. I got a ticket for the last Saturday night preview. My experience in the past is that getting good tickets to any preview performance, particularly Saturday night, was a challenge, but not today.