All this is well known. You're not getting my point. Please check for areas in Manchuria under Qing rule. It's an unspoken tenet of the CCP to claim all areas under the Qing rule. That includes Port Arthur and other areas lost under Qing rule to the Russians. Add to that a lot of Chinese immigrants in the Russian far East, outnumbering the Russians and you can sense Russian unease .They highlighted it a while back mate.
Sino-Soviet border conflict - Wikipedia
China has easier pickings without annoying their closest ally.
There is mutual mistrust between the Chinese & Russians.They aren't natural allies. What brings them together is a certain anti Americanism which in the case of the Chinese is inevitable given their spectacular rise and belief in their manifest destiny of being the premier power in the world. The Russians are hampered more by a Cold War mindset among a significant section of the US politicians plus a weakened economy making them dependant on the Chinese.
I'm waiting for a Kissinger moment to right the relationship with Russia. It would have happened under Trump except that he's too compromised by his dealings with the Russians to attempt something like that. Perhaps in the near future.