It is not a switching issue, it is a known game issue (bug). It has a chance of happening equally in singleplayer and multiplayer...
I hope Patch 3 will come out any time soon and fix everything
Honestly:"The game is the best in the genre" especially the tons of units on a huge map while the game remains playable..
and the AI is actually really good now, he really wage war with huge numbers during any invasion..
But, even the best is not without mistakes.. So I really hope they're going to fix them any time soon..
For me the biggest problems are:
1) Stacking/Stucking problems
2) AI sometimes spreading forces around the world not properly! ( France has tons of units in my game.. most of them in colonies..
wiping out France would be easy even for the Netherlands because before those units in the colonies return, the dutch are already in Paris! For this I posted an advanced combat theater system on the forums already. Where I as user, but also the AI of course, can prioritize theaters, set numbers of units for every theater, and form armies which can be pointed strictly to any given theater, and thus never leaving them undefended (as in my game France and UK are)
3) AI's should have some code implemented to strive for self-sufficiency. Right now, even small nations can beat bigger ones.. The human simply goes for self sufficiency.. build more land production etc.. the AI just sits there as a sitting duck.. and once you made yourself a big enough industry with military capacity, even Belgium can beat Germany then.. So it's kinda weird actually..
4) This mentioned in the forums already, but very annoying to me, countries I've annexed, remain "hidden" in the game.. or sometimes some plot is suddenly pointed to a just conquered nation.. You can click on that plot.. You can declare war on it, but nothing happens.. It remains there forever..
5) I also had the experience(probably the same error as in 4) that I just conquered lands of Russia's colonies.. Then he offered me peace.. I agreed.. The lands were mine, but not really. For some reason, the Russian AI kept controlling those lands as well!
Loading the game as MP, and taking over Russia as a human player disabling the AI from garrisons I could put garrisons on those plots.. If I enabled the AI to control garrisons, he kept putting them away on territories conquered by the other PC..
I think there's a general error where (once a nation has lost something) not every coding object is reset to the new owner, and this manifests in the game on different weird things that happen, but basically it's the same error, that's what I bet..
Those are the only major points I have at the moment..Many other things can be improved of course..
Things added:"like a more complex industry, more raw materials, gold, iron, steel, etc.." but that's not important for the game any time soon..