I got a similar bug report from a different player who grinded the first level to increase the shop level. I'll need to look into what makes this happen, I mostly just went through all of the four levels in sequence when I tested them. Thank you for reporting this, now I know that it's unfortunately not too rare of an occurrence.
There are 2 sexy events in the game right now, the first of which occurs at the end of the second expedition and it does feature Boa. I hope you'll get another chance to see it!