This would be due to not just the 2 or more dc/leaves but the repeated history of issues you've gotten with your connection. Just because you didn't dc/leave more than those 2 games doesn't mean you're issues weren't affecting everyone else all those other times you had issues or were afk/idle. Leaverbuster has built in leniency and a lot of it to ensure that when those occasional rl issues come up storms, family etc you don't get penalized. To get to that 20 minute queue means you've used up all the built in leniency and then some.
Leaverbuster tracks not just leaving/dcing but also time spent idle, running around in game not doing anything, sitting in spawn endlessly, sitting in spawn just buying/selling items etc. As an example lets say you start a game every night at 5pm but then every night at 5:10 pm you go afk for a few minutes to put your laundry in the washer and then do it again alter for the dryer. Well the system tracks this and notices a pattern and starts dinging you with what we'll call penalty points.
Once you've gotten enough penalty points the system sends you a punishment until your penalty points decay which happens by not doing those things that earned you those penalty points. In your case you didn't get that 20 minute queue penalty because of those 2 issues but because those 2 issues pushed you over the limit. Think of it as the straw that broke the camels back so to speak. If you play games without issue then your leaver level/penalty points level goes down and you get reset back to zero and get your leeway back.
I've had the firewall bug quite a few times as well as the occasional rl emergency and power failure, isp issues etc and yet in over 3 years of playing have never gotten so much as a warning or timeban. Most of the community is the same way since it doesn't happen often enough to get us into trouble. In your case something is triggering Leaverbusters warning systems to flag you and you need to figure out what you're doing that's causing this.
Make sure that when you're queueing up that you're leaving enough time to play and not say taking out the trash, getting dinner, bio breaks (yes I know but those can be planned around usually), doing chores etc. If you're getting up to do something while playing constantly then you're going to keep getting punished with queue timers. Since you're affecting up to 9 other players game as well as your own.
You can always check with support and ask them what's getting you flagged so much and perhaps they can give you some hints or a general idea what to fix.
