I've been having similar issues and currently I am on a 10 minute leaver buster because my game freezes mid match and I have to restart my computer to rejoin. I play in a 5 stack most of the time so my absence doesn't really bother them and they understand.
I am in the process of fixing my issue with my computer with the assistance of Riot Support and once the issue is resolved I will ask about getting these penalties removed, maybe that is something you could look into? I suggest making a Support Ticket.
Best of luck !