I'll go first. I'm learning German, and I said "ein App" instead of "eine App" twelve times in three days. ChatGPT corrected me every single time. Every new session, it forgot we'd already been through this.

I think everyone learning a language has one of these. A mistake that survives every correction, every app, every teacher. Spanish learners mix up ser and estar for years. French learners guess genders forever. In English it's prepositions ("depends of", anyone?).