Is there a reason why Le Bot never disconnect using one of his bots, but disconnects using a .dmbot file?
Yes. As I have always said to people, actual in-built flash bots are much more stable compared to those created in the Bot Manager. The advantage to flash bots is that there are a lot less disconnections as long as it's made correctly, but the disadvantage is that it's not so accessible and there are a wider range of options with the Bot Manager. It's just what you prefer I personally use the in-built bots and only very rarely use the .dmbot files :P