I'm running into 2 significant issues with Diplomacy:

1) I'm unable to propose any diplomatic offers to the Lumeris. I can click to add things to the offer pane and see the chance of acceptance (and the available offers in the case of adding Peace) change, but nothing shows up in the offer pane and the "make offer" button stays grayed out.

2) Literally no offers show up with the Unfallen, currently my allies. Nothing in the pane at all.

Save link: https://drive.google.com/file/d/19kmjxLVNoFzYHXkm-_CljrWlGqfmeLRo/view?usp=sharing

As I've continued to play on that file, the issue has been inconsistent. Now on turn 146 after a war with the Lumeris (which they declared) and having added the Riftborn to my alliance, diplomacy appears to be working normally again. 

Here's a newer save link - not sure what changed, but maybe the code folks can find something underneath the surface that's different. :P

https://drive.google.com/file/d/1fT5o7jWWjxacsv7LYfKK5zIqDkZlQS58/view?usp=sharing

EDIT: Also for what it's worth, I'm running Vaulters and Umbral Choir expansions - not running the Behemoths or the new one.