To reproduce in singleplayer:

Build the attached design (first screenshot, or third screenshot for a design that doesn't depend on BUDs), flip the lever on. Note: The piston is a sticky one. The piston should extend and retract quickly.

To cause the bug, either

• die
• alt-tab out of minecraft for some time
• save, exit to menu and reload the save
• just wait, walk/or look around as it seems to happen randomly, too

Actual outcome:

• The piston is still pulsing, but the piston arm and the pushed block is invisible (picture 2)

Expected outcome:

• Piston arm still visible