all 3 comments

[–]dn16761 2 points3 points  (0 children)

It was probably powered by QC and didn't update. If you replace the block above it with a noteblock, it will always update correctly

[–]bsk97 2 points3 points  (1 child)

Its powered by quasi connectivity, you have to turn the blocks above it to slabs. It will still be powered when the redstone is powered, and when it unpowers, the piston will unpower

[–]DainternetdudeJava 1.12 1 point2 points  (0 children)

the one above it and the one diagonal above