similar boat here: what I’ve noticed is that, on your instance, 'foreign' toots will only show the favourites coming from your instance. So, if 3 people from your instance favourited a toot that has 1500 favs total, you will only see 3 next to the star

this isn’t true for boosts, and I don’t know what causes the difference there. Its probably something to do with an incomplete federation (either because of blocks or simply because your server isn’t aware of all the others; I’ve noticed that the difference is much larger now that I’m on a smaller instance with less connections), but I’m not sure

for toots coming from other people on your instance, you will see the full count on both favs and boosts