This is not a bug. I believe it is related to current situation with average k/d majority of players has(approx 2.0) and huge gap in k/d some players are already reached(3.0 and more). I don't have access to solid statistics but according to similar problem i heard from particular players (Nekomant, FunkyColdMedina) I believe that after MM changes which came with latest update we got into some sort of hard "improbability conditions", that makes us(people with high k/d or amount of Total battles) virtually isolated from any match no matter what ship tiers or fleets we choose.
That wasn't unexpected of course. And for a solution I'd like to propose stats reset. It won't mess much with balance because many people are already have t3 and t4 so we will be pretty much close to old pre-progression competitive battles(which would be gladly welcomed these days), where ships are equal and fun available for everyone, not just majority. Also skill are growing faster when playing against strong opponents, not strong ships.
Currently we are testing this "k/d hypothesis" with smurf account. Trying to reach perfect k/d and see how MM waiting increasing and how soon it will be impossible to join at all. Better if developers confirm it with proper data and tools. We are kinda limited here after all.