Solved
Feeding a cowplant only satisfies hunger if the "cake" is visible.
Product: The Sims 4 Platform:PC Which language are you playing the game in? English How often does the bug occur? Whenever you feed a cowplant before it's hungry. What is your current game versio...
Okay, with further testing I'm not 100% sure my initial observations hold. I still think they're getting too hungry too fast! and faster than they used to! and did have a cowplant stick out its tongue IMMEDIATELY after I fed it without the tongue visible, but... it instead seems to be completely random where instead before I thought there was more of a pattern. So I'm going to mark this as the solution (such as it is).
(Basically: Feeding not topping off hunger is probably a bug. Changing the rate of hunger decay to possibly be an RNG rate is probably an intentional development choice.)
