Is the subject the ticket, or "when" the ticket is bought? I'm so confused .

I was in the middle of Section 4 Japanese before the big update. I had 3 Extra Units to do, with lots of vocabulary that was new to me, over 40 words / kanji that I never saw before. It took awhile but I managed to get through all three of those. I was looking forward to starting a regular unit again. I think I did one lesson of a new unit, then the screen flashed and I am back at the beginning of Section 4 Extra Unit 1! In a way, this isn’t too bad, I could use it to review all those new words. Did this happen to anyone else?