I believe this is now my worst loosing streak in Ranked ever, and I'm pretty confident the game was in error in placing me in Platinum League Tier 2.
I decided to go practice a bit against the Elite AI next.
I then went and played a single Unranked match:
Finally snapped my lengthy Ranked loosing streak!
In a patch yesterday, Blizzard Entertainment fixed the leveling and progression in Versus AI, so I'm going to battle my way up back to max difficulty: