So I'm trying a game as Portugal and taking the monarchist path. I get to the point where I trigger a civil war in Brazil, which had gone Democratic. It is May 5th, 1937. Things start off fine - Empire of Brazil gets most of the Brazilian military and my troops are crossing the sea to help. 8 days later on May 17th, Empire of Brazil ceases to exist. I tried reloading a save and it does the same. I even go into observer mode, switch to Empire of Brazil to see what is happening. At 1am on the 16th of May, it stops showing the two sides as red to each. 1am on 17 May, I spontaneously get a game over screen.

I could take the time to use Portugal to conquer Brazil on its own, puppeting it and (in theory) making it eligible for the merge focus, but I would love to know what is going on that is making me go to the extra trouble!

Google searches don't seem to be answering the question - has this been happening since ToA?