I was mining with an efficiency 5 diamond pick and haste 2. In other words, super-speed mining

I thought that all the blocks would mine at a super-speed

Some of the blocks like those in the attached screenshot were being mined at normal speed.

1. Make a double beacon with Speed 2 and haste 2
2. Get an efficiency 5 diamond pick and name it.
3. Start mining in a sweeping pattern.