When sending a redstone signal into a block, the block gets powered. If a Piston or Sticky Piston is placed next to said block in any direction except towards the block, it extends. However, if a Piston or Sticky Piston is placed below the powered block, facing upwards, some Pistons act on a one redstone tick signal (for Pistons the length of the signal does not matter, for Sticky Pistons it means they push a block but leave it, or extend and grab a block if they don't currently have one).

To reproduce the bug, see the images, along with the instructions:
Place the Emerald Block at exactly XYZ (62, 58, 7), and extend the "arms" in all four horizontal directions. Then place Sticky Pistons facing upwards on the 3 remaining sides (excluding above) of the Stone Blocks above the already placed Sticky Pistons. Place Dirt Blocks at coordinates XYZ (61, 60, 10), (58, 60, 7), (59, 60, 6), (61, 60, 4), (63, 60, 4) and (65, 60, 6) and Stone Blocks above the remaining Sticky Pistons. When placing a Redstone Block on the Emerald Block, you may notice that the Dirt Blocks get lifted, and left in the air, while the Stone Blocks stay still. (The bug is not exclusive to Stone and Dirt blocks, they were just examples so you can see that the result is predictable, regardless of seed)

The bug can also be seen with the Emerald block at XYZ (69, 56, -10), but with Dirt Blocks at XYZ (65, 58, -10), (66, 58, -11), (68, 58, -13) and (70, 58, -13).

Currently, through testing, I can say that the bug is affected by:

• Coordinates (X, Y and Z)
• Placement of the Sticky Pistons around the powered block
• Direction the redstone signal enters the powered block

However so far it seems to ignore some factors (I do not have 100% confirmation as it could just be a coincidence):

• Rotation of the Sticky Piston next to the powered block
• Strength of the redstone signal (assuming it powers the block)
• Version (I discovered it in 1.16.3, but it seems to have the same results in 1.16.4, however I can't seem to add 1.16.3 in the Affects Version/s)