I'm definitely getting a kick out of this mod, but after 2 games playing until 1943 I'm noticing some annoying problems.
First is that if Czechoslovakia is Paternal Autocrat (via elections) it seems to like leaving the Allies (after the event that brings them and the Poles into the Allies) if there doesn't happen to be a war on. Second, Poland apparently likes to leave the allies, too (this happened my second game). This generally results in the USSR declaring war on Poland eventually. However, since France and maybe some others have guarantees on Poland, this can result in a declaration of war by France or someone else on the USSR, which starts to make things get kinda sloppy in terms of AI behavior and events. However, the event regarding the war in Poland (with the option "stay out of it" being the only option I as germany had) that fires for the UK, France, and Germany causes any of the aforementioned to leave their alliance (resulting in the Allies not including the Brits and French, or germans for that matter)
Since in my second game by the time war came to Poland, Japan had already initiated war against the US and the allies, this created significant difficulties. First, the USSR doesn't seemingly care they've just signed a peace treaty with you, they'll just declare war now that you've just left the allies and are bereft of friends because of the goofy events that months or weeks earlier saw you in an alliance but have now forced you arbitrarily out. Second, since the "allies" were briefly at war with the Soviets, that means, say, Czechoslovakia is still in the war (if they joined/stayed in the Allies), along with every other allied nation but those that got the event that concludes peace with the soviets/tells the country to leave their alliance (at the moment, Australia is the leader of the allies). Third, although I'm at war with Japan "together" with Britain, France, and the rest of the gang, since I'm not longer technically a part of the allies, I don't have military access, and so my fancy new kriegsmarine (with two carrier task forces and two surface action groups!) is useless since god knows a powerful navy doesn't really help much against the USSR.
tl;dr the war/peace events surrounding going to war with the USSR over Poland are a little sloppy. 1. make anti-soviet alliance with Germany, Poland, and Czechoslovakia. 2. Poland and Czechoslovakia like to leave the alliance depending on their government type (or whatever other invisible factors there are). 3. War happens anyway. 4. Ensuing peace events are for individual nations rather than the entire alliance and can make it more likely for the USSR to expand aggressively even if Poland isn't yet annexed.