Got 14 cheeses but only saved 12 mice.

-rant-

Were two saved via heart?

Probably

Did they change it or what?

Ah no, just been a bug since the beginning of the skills; mice saved via heart dont count as a save

I don't have the skill in question and this happened to me as well a couple of times lately.

yeah was playing with someone and they had a similar issue, no hearts or revs used so idk

i remember this bug popping up last year when i played. It only happens in large (11+ mice where first counts) rooms as far as i've seen, if that helps