"My hands got tired because I carried a heavy bag."
This seems like less of a "because" scenario and more of a sequence of events.
The "because" is implied here.
True, it's more like "My hands got tired carrying a heavy bag." While the Japanese sentence is fine as is, the explicit 'because' in English trips you up. To have it to be more of a sequence of events with an implied 'because' in English, the translation would have to change too.
I disagree with this translation. The use of "because" wouldn't be needed unless it's describing a direct causation between two events. Implications (as in the absence of because) would also imply that other causes could exist. Without から present, the sentence seems more like "my hands got tired after I carried a heavy bag." Notice how there's no indication of direct causation. This is what because is for.
Then it would be motta, no? Also not necessary to use kara when this way also makes sense.
In several last lessons some audio is always missing. Even if I always report it it seems to me that audio is missing intentionally...