This is happening across several platforms, my friend on pc is having the same issue. Any large worlds are no longer saving to the cloud due to the size which seems to have grown exponentially. I can no longer play on any of my main worlds and save any progress as anything saved locally will eventually be overridden by the cloud version of the save. This needs to be a priority as we can barely play at all due to this issue.
This issue is being tracked at MCPE-217104. Also, there are no cloud saves on PC, so it is not possible for your friend to be experiencing this issue. They are experiencing some other issue.