That is, you want to say that the moderators suddenly began to delete half of what is published there? The difference in calculations is 3-8 times different.
As I said before, topics moved/deleted don't have to be new ones to affect post count difference, inactive old topic from few years ago that got moved will affect numbers. My assumption that such a big difference is probably caused by mods work is based upon previous experience in similar situations.
Year ago, while working on one of these overviews, I noticed that Arabic board ended up month being in negative of ~200 posts. Since i was relatively new to Merit Dashboard and didn't really know how it works but kinda wanted to figure out what happened there, I contacted one of their active members asking can he maybe explain the situation. He contacted their mod who eventually contacted me, explaining that he indeed did some cleaning and moved/deleted some topics, causing this anomaly. Similar thing happened to Croatian board 6 months ago when we got 2 new child boards so bunch of topics were moved around and merit dashboard showed us having 1/3 of the posts that were actually written.
If you really wanna get to the bottom of this, I suggest that you ask your mods about it, and if they really confirm that they haven't moved anything around, that would leave us with some glitch affecting Russian local board numbers.