EDIT: as of the most recent Bedrock preview, this issue is no longer the case, as they have changed Bedrock to match Java. For posterity (and because I believe removing these blocks - particularly Sand, Red Sand, Gravel and Sculk - from Bedrock’s tags was a poor choice) the text of the issue as it was remains below.
Several blocks which can be swallowed by Sulfur Cubes on Bedrock Edition cannot be swallowed by them on Java Edition.
Below are a list of these blocks and their respective archetypes on Bedrock Edition:
Bedrock - Regular (would likely be changed to Slow Bouncy since its addition)
Sand - Regular
Red Sand - Regular
Gravel - Regular
Ice - Fast Sliding
Reinforced Deepslate - Regular (would likely be changed to Slow Bouncy since its addition)
Sculk - Fast Flat
Redstone Block - Regular
Slime Block - Fast Flat
Honey Block - Fast Flat
Many of these blocks not being swallowable by Sulfur Cubes on Java Edition feels more like an oversight than intentional design, especially since it’s different on Bedrock Edition. Since this is a new feature, I believe this is a valid parity issue.
Steps to reproduce:
Locate or spawn a Sulfur Cube in Java Edition
Attempt to place one of the above blocks inside it
Note that it will not accept the block
Locate or spawn a Sulfur Cube in Bedrock Edition
Attempt to place that same block inside it
Note that it will accept the block
Expected result: The two editions have the same list of blocks acceptable by a Sulfur Cube
Actual result: The two editions differ in this regard
Resolving as CR as you’ve stated the issue is no longer the case.