You need to change your 'angle', but if you take a funny slant when looking at this (and prepare ahead) this can be used to your advantage.
The units are showing up just as Wyatt explains - backed up reinforcements. Yet when they appear, they are generally glowing cherry-red, are out of supply, etc. With borders turned on, it is easy to see where these units appear. It is a pain to be fighting large amounts of Russians in 'controlled' territory - for sure. Yet it generally takes you only a small fraction of the forces it would require to deal with these units were they on the front-proper. They can generally be encircled with little effort, (you go first, remember), and take almost nothing to collapse the pocket once you form it. There
is the chance that some of the units are not reconstituting, but appearing for the first time - ie: they are fully rested. This doesn't happen often, and when it does, you just display a little patience and keep him in the pocket til he's red. If he tries to break out (and even succeeds), that's fine too - he is now much closer to red, and you simply re-encircle him.
You collapse the pocket for very little losses - yet the Russian equipment tells a completely different story. They were out of supply, so those thousands and thousands of squads saw
none return to Russian stockpiles. Those squads are enough to reconstitute a small army in russian-held territory, and now they aren't available. Lets picture a game where you have 3 large-scale events like this - that can easily be over 10k squads...
No, this isn't perfect, and I don't say that anyone should like it. Simply pointing out that since 'that's the way it is', a German player can still act to turn the lemons into lemonade.