I figured it out! For some reason, every BFAV pack I downloaded had its JsonAssets objects in a folder named lowercase-o "objects", so JsonAssets wasn't recognizing them, causing issues with both BFAV and PFM. Changing the folder name in each pack to uppercase-O "Objects" fixed it.
Thanks for letting me know!
It was indeed "objects".
But could not be resolved...
In my case, I only fixed it as follows:
[JA] Trent's New Animals Pack > objects
↓
[JA] Trent's New Animals Pack > Objects
I restarted the app after doing so, but the log displays the same message as before the response.
And as usual, animals added in mods don't produce items.
What would be missing from my procedure??
※Also, even if I corrected the "Objects" folder of other JA folders to "objects", it worked without any problem.