I'm having trouble reproducing the bug with impossible peace deals, so I'm gonna ask for some community help here. 
If anyone could replace the DLL and PDB files in their MODS > (1) Community Patch folder with the ones I attached to this post, use no other mods, reproduce the bug, then send/post a save file, it would be much appreciated and I could debug the problem instantly.
Unfortunately you need the debug DLL to run the debugger, and savegames from the release DLL (which is better optimized) are not compatible with debug DLL saves.
But if I'm given a save file that uses the debug config, I can run the debugger and instantly figure out why it's malfunctioning.

If anyone could replace the DLL and PDB files in their MODS > (1) Community Patch folder with the ones I attached to this post, use no other mods, reproduce the bug, then send/post a save file, it would be much appreciated and I could debug the problem instantly.
Unfortunately you need the debug DLL to run the debugger, and savegames from the release DLL (which is better optimized) are not compatible with debug DLL saves.
But if I'm given a save file that uses the debug config, I can run the debugger and instantly figure out why it's malfunctioning.
Let me know if it's still necessary and I'll keep the debug settings for when I play next. (Computer seems to be able to handle lower performance just fine)
. But really, barbarians being able to heal sounds great from both a flavor and a balance perspective given how easy it was to wipe them out with 3 warriors and a scout tops even with raging barbs. Nice to see they're actually going to be a bit more tenacious and more of a challenge to overcome instead of free experience (and yields).