Looks like a shaky connection to me.
No, It was a stable 4G connection.
Then it would work as well I guess. This could be triggered if the read timeout has been triggered. It's triggered if a read operation takes more than 10 seconds to initiate. What ftp connection type are you using?
If your connection had more than 10s read timeout, then that would trigger this. I think 10s is an extremely long time. Increasing the timeout is possible, but usually gives a worse user experience when there is a definitive connection break.