There is info that the troops didnt think they were invading. They were either thinking they were protecting against nazi troops or were just training.
This makes sense, if you're planning an invasion, the troops cant be told. They would be security threats.
But at the same time, that lack of knowledge will make them ill prepared at the beginning. But their morale after these massive losses will suffer.
The thing is about proxy spec ops. It's practically 100% they are there but russian troops cant be told. Imagine you're already taking losses, then you get told the world's spec ops are there. You'd shit your pants. You're figthing against farmers and navy seals? You would have to treat every fight like you are fighting navy seals. That would make anyone rout instantly.