The bug is back. In fact I think it never gone , just because it's not so easy to reproduce it., the last update just moved the problem "2 months" later.
I started a new game with DLC and no mods (but easy dev and fresh of course) on a vanilla map (the basic US one). Created chicken park and kept the small cows pasture, gave food/water to let animals having 100% health and then slept a month. Animals became older without trouble. Save the game. Slept another month, everything was all right, baby chicken etc... (october). Slept to november and here nothing had change. Chickens are still 8 months, babies 0 month, cows 52 etc...
I don't know if it can help you but I saw this error after sleeping:
2026-02-17 11:47:51.881 Error: Running LUA method 'update'.
C:/Users/.../FarmingSimulator2025/mods/FS25_Fresh/scripts/core/RmLossTracker.lua:192: invalid option '% ' to 'format'
It looks like your mod "freeze" the natural evolution, even the mod "redtape" is impacted, active contracts and policies become muted.
I believe you'd be able to reproduce it (I retried without DLC and easydev with the same result ).