Client specific behavior can't cause server-side abnormalities. There is no difference between a client connection and a raw telnet connection in regards to how it affects the CF servers.

I'm not saying somebody's client couldn't be causing a problem on their end, but if the bug exists (haven't played recently enough to know), it's not going to have anything to do with a particular client.

Additionally, there is nothing CF could rarely send to make people not see particular combat rounds. So they'd have to have some sort of trigger/gag doing that.

Sounds promising right? Two problems with that:
1) It's going to be consistent. It'd take a very deliberate effort to gag certain combat rounds and not others, impossible to do by mistake.
2) If that were the case (or in the case of packet loss), then in the logs sent claiming to be an example of the lag bug, they'd be missing hp (at least some of the time, if they don't block everything) from the round that happened but they didn't see. From what I've seen people sharing, that isn't the case.