[Alex]

The big problem (and I haven't read the science nitpicking spoilers) are, and I could easily be wrong:

Spoiler:

Items in the same orbit are going the same speed or they wouldn't be in the same orbit. So that cloud of debris shouldn't hit them multiple times.

In the real world Hubble, ISS, and the Chinese station would not be both in the same orbit as each other and within a hundred miles of each other.

Communications satellites are in geosynchronous orbit at 22,000 miles. ISS and and Hubble are in low earth orbit of just a couple hundred miles. The same "chain reaction" couldn't have taken out both them and communication satellites. And again it isn't like all the communication satellites are holding hands, one debris cloud up there wouldn't take them all out in a couple of minutes, especially if it then had to descend into a new orbit 21,500 miles lower two minutes after that.

Why was the Chinese station losing altitude?

But I've seen Cuaron quoted as essentially saying "I had a story I wanted to tell and it could be told with real world orbital placements. So I put everything in unreal orbits and told the story."

I'm ok with that.