So I've tried cleaning the nozzle at 250°C with a string and pushing a lot of filament through it, however that didn't help: The surface was just as bad as the 3 prints earlier.

But then I've decided to check the moisture "theory". I've baked the filament in an oven at 70°C for about an hour and the magic happened .


Here are the first 3 prints again:
3_prints.jpg

And here is the same object printed with "baked" ABS:
baked_print.jpg

I guess next thing I will buy is some tupperware container and kitty litter to keep it dry

However, the other issue I've had, with corners not being square but having a small blob on them still remains :\ Any idea what might cause that?