MC 1.16.5
Excepted: https://www.youtube.com/watch?v=aXT0PFx0hTE (doesn't happen with Quick Mode enabled)
Actual: https://www.youtube.com/watch?v=SIGBgAet7B0
Replay: https://cdn.discordapp.com/attachments/709108200632483900/941217662770507776/2022_02_10_08_16_11_1.mcpr

Don't see anything wrong with the replay data, nor can I think of any way for this to be broken by the cutting code (and no original replay was provided for comparison), so I'm just going to assume that this is simply vanilla behaving as programmed in the presence of a bedrock breaking machine.

The reason the blocks don't break in Quick Mode is that it doesn't support explosions at all.