It seems like pistons are not getting extended, when they get a short (0-tick) redstone pulse from north-south or south-north directions.

Pistons do get extended, and "spit out" their block in the west-east and east-west alignments, as expected.

And there's apparently a bug in here somewhere. Either both or none, should extend.

Redstone lamps light up like they should, so it's not about power not getting through.

Doesn't matter if the pistons are regular or sticky.

Even pistons facing vertically are affected, so the bug must be about powering the pistons somehow.