What's observed:

Sand/Gravel blocks break when an retracted piston block is pulled down from underneath it

What's expected:

The sand/gravel block should fall normally and not break.

Why this is an issue:

This behavior is new to the 1.16 nether update and has broken the redstone door, shown in one of the videos provided, that I use in many of my builds.

*videos below demonstrate the issue with sand blocks. The result is the same for gravel/red sand/concrete powder as well, though not shown.