It is impossible to break an armor stand with any tool in this snapshot. It works fine with your fist but it won't break if you're holding a tool. This is in a singleplayer world.
Linked issues
Comments 2
I'm resolving this as a duplicate of MC-268800. Double-clicking breaks the armor stand as it always does, so some tools not breaking it immediately is most likely thanks to the reduced attack damage from that bug.
Probably caused by MC-268800, if it's not even the same issue.