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If you have regular internet connection issues, Leaverbuster will get more and more harsh with the bans. It's an automated system that only takes into consideration disconnects and AFKing, and, as far as I know, does not take reconnecting back into consideration.
Leaving once in a while will never get you banned by Leaverbuster, but if it becomes a regular thing over time or a sudden spike in a small sample of games, it will kick in. The more times it kicks in, the harsher it may get.