Maybe because my Gurus were also leeches? I had the same items coming back and back, dropping to Apprentice, getting them to Guru again just to drop again when I messed up.
I noticed that also out of 70 Apprentice 60 were Leeches, and for the Guru it was way more than 50% as well. So that’s when I knew I was hitting a wall and if I do not get my Guru items down (and tackle my leeches), I would at one point just give up.
But yes, until level 17 I just took all lessons at once, which totally backfired now, because there were days when I had hardly any reviews and suddenly 200 extra burns were there. After stopping new lessons for a month and really focusing on leeches now, I am at least back to 200 reviews a day and not 400+ anymore. Too many reviews made me lose my concentration and even more mistakes happened. Was kind of a viscous circle.