The Bug:

Neither command blocks can change a player's gamemode in hardcore mode nor you can use chat commands to switch gamemode in hardcore mode with cheats somehow enabled one way or another, being inconsistent with Java Edition. 

Steps to Reproduce:

For this bug to work, you must either have a release version of at least 1.21.40, or you can use the latest preview.

1. Download the attached world. The map starts in creative, default gamemode is creative, and the map is in hardcore mode, and cheats are also enabled, which is normally impossible. This world was created to test this bug. Cheats were activated via another method other than external editors, and were not activated via MCPE-180404.

2. Use the lever to your right. That will attempt to change gamemode to survival hardcore from creative hardcore, but the gamemode won't change at all.

3. This step is optional. Since the attached world in creative hardcore mode will also have cheats enabled without using MCPE-180404 to activate cheats, you can also try to run /gamemode survival @p

4. Whether you tried step 2 or step 3, gamemode switching is unsuccessful, because even though this attached world somehow had cheats and is a hardcore world, gamemode changing with commands did not work. 

Expected Results:

Command blocks will change a player's gamemode in hardcore mode with cheats somehow enabled one way or another, just like Java Edition.

Observed Results:

Command blocks are unable to change a player's gamemode in hardcore, inconsistent with Java Edition.

Notes:

This bug report does not not talk about how cheats were activated in the attached world, as I did not use MCPE-180404 to enable cheats on this now creative hardcore world, even though cheats are present. This glitch does not occur on non-hardcore worlds as far as I know.

• Even if cheats can't work on hardcore at all, because it is a creative hardcore world there are still command blocks that can be used in the test world to try to change the player's gamemode without success.
• In the test world, using the left lever will attempt to change the player's gamemode to creative from the left command block. (the player already starts in creative)
• In the test world, using the right lever will attempt to change the player's gamemode to survival from the right command block. Because the test world is a creative hardcore world, the attempt will fail, and that is covered in the reproduction steps.

Parity criteria met:

• Hardcore mode exists in the latest release of both Java and Bedrock. (Java 1.21.2 and Bedrock 1.21.40)
• Hardcore mode was added in Preview Bedrock in the first 1.21.0 preview, and was added to release Bedrock in 1.21.40 (Bundles of Bravery).
• Somehow in hardcore worlds with cheats enabled one way or another, commands from chat as well as command blocks both can't change a player's gamemode in Bedrock. In Java, hardcore worlds with cheats enabled one way or another can use commands from chat and command blocks to change a player's gamemode.