Sorry for the late reply!
SPOILERS
It was actually the step of going into the portal! I'd figured out that I needed to write the portal code on the door using the yellow lipstick, but it took me ages before I figured out I needed to put "write symbols." I did try "write portal code" a few times because that was what the scrap of paper/diary said. I also messed up thinking that I needed to specify what I was doing it with and putting "with lipstick"/"with yellow lipstick" a couple times. Once I got it, it felt kind of obvious, though! I'd say that the main thing you should maybe consider is allowing "portal code" instead of "symbols." Thank you for asking :)
And now I'm also gonna add some unrelated things that I left out of my first comment because I didn't want to spoil anything there! So... still SPOILERS!
I really liked how some of the puzzles made me really go "ohhh!" Like how when I first opened the closet and saw the broom, I was like, uh, okay, but then as soon as I tried to take the necklace and it said I couldn't reach, I was like "Ah! The broom!" And then also with the rag, I kept trying to wipe the smudges off at various points through the game, but then when I reached the moment I was actually supposed to, I was just so excited. PLUS, I was carrying the scissors and the fake protection charm and the garden shears and I wasn't sure what I was going to need any of them for, but as soon as I realised, it felt so cool.
Okay, this comment is getting a little long, but I also wanted to say that the only thing I ran into that felt like a "bug" was that if you try to use the garden shears or curling iron at the sliding door after you've already burnt the flesh, it still goes to the same scene bit as if it were still there. (Found this out because I, for some reason, thought, "Hey, maybe I can smash the glass door with the garden shears?")
Thank you so much for making this cool game! AND for replying to my comment! I really appreciate it. :)