paoloberlanda wroteI’m writing chords with notion on iPad using Apple Pencil. Notion changes the notes of the previous chords apparently with no reason. Anyone experienced the same issue?

Yes, and with individual notes as well. It seems to me that occasionally Notion gets confused about the tuning of the selected instrument track. Example: tonight I was inputting an oboe part when suddenly the whole measure I'd been working on, and which had been correct, jumped up a 4th in pitch. Worse, while I could correct those changed notes by clicking and dragging the individual notes, every new note I added via Handwriting was instantly shifted up that same perfect 4th. I had to switch to having another track highlighted and then go back to the oboes, which seemed to "unconfuse" Notion.