Having seen the code for this mod, I don't see anything that would cause a bug from "inside" the mod - all it really does is increase the numbers from "1" to "10" or whatever the amounts are.
That doesn't rule out of course some wierd interactions with the happiness system itself - the system is hardcoded so we really don't know much about how it works, perhaps it can't handle numbers bigger than a certain point? Who knows... well, the Devs do but they haven't said anything
Townie deaths usually have a lot of knock-on negative effects, for example the stink clouds and corpses also lower happiness as well as the "death scream" itself. It can be hard to tell what's causing a happiness drop, since it could be as simple as one townie is constantly working because they randomly get assinged all the work. That would have a significant impact on the average happiness - if they have 0 and everyone else has heaps, then the average still takes a massive hit.
Even with the original mod installed, the food boosts won't overcome any serious negative influences like overworking, lack of food, "negative decorations" etc. Unfortunately we can't just let the townies idle to fill up their happiness anymore, and it's almost impossible to check that every townies has their work:idle balance right... you could put them al into food production and make it so they have enough jobs to keep exactly half of them busy at once, which is about the only way to make sure you have no negative modifiers active from working/resting too long, and then see if they're still not regenerating happines like they should.
What's that you're eating? A nice, juicy apple? You weren't supposed to eat that you fool, you were supposed to make it into a pie! - last words recorded words of Francis D'Avre before he went looking for snowcherries, but found a hungry Yeti instead.