Good catch, that was it indeed! Funnily enough, the practice.xlsx file I sent was in fact a debug version of the full file, with 1 practice trial instead of 16, which I had created while trying to solve a different problem (to which sadly I got no reaction). It seems a change in the number of rows of the conditions file makes psychoPy stil expect the same number of rows, with this error coming up if that number has changed.
Incidentally, I would point out it’s quite confusing that psychoPy reports the number of rows in a conditions file as “conditions”, since as I understand it, what you normally have across rows are raw trials, a number of which are typically repeated within each (actual) condition.