After updating QGIS i found that wmts layers are being rendered in way that makes them useless. It look's like tiles are downloaded in greater resolution and then scaled down what makes them rough and all captions unreadable.
I'm on windows 10.
Ok some more digging with other keywords gave me the solution:
It's related to the scale of layer in viewport. There's a plugin called "Tile map scale" which helps put map in to scale that provides best quality. You can also change qgis scales in map setting to values that ensure proper rendering.