I read a book where the author I generally liked (Phil Rickman, I really recommend December https://www.amazon.co.uk/December-Phil-Rickman-Standalone/dp...) used past tense but for a new book switched to present. It really jarred and I had to make several restarts before I got into it, and that only happened because my brain learned to discard the tense (edit: several retries over a period of days; it wasn't quick).

I guess the theory is it makes it more dynamic, now-ish. In fact it just seems a trivial affectation that ultimately adds nothing.