As you can see in the attached video, if you run a command that has dx dy dz and also uses xyz as ~~~, the area you select will go out one block further then intended (notice the comparator activating even when I'm not in the area specified by the command block). (also shown in the video halfway through) If you use actual numbers instead of ~~~, then the issue doesn't happen.
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duplicates 1
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It's caused by how the location for the command execution is chosen. If we don't provide any decimal value to the coordinates, it will run the command from the center of the block. Which isn't how it worked before when selecting entities using the volume
Anyways, when we set the distance value, the command will take the center of the block diagonal to our main block, so it can have a single block volume as the initial space. This shouldn't cause any issues, IF IT WAS WORKING AS INTENDED. But here, it will just create a block range that is on an offset of 0.5 block towards both the +X and +Z axes(I didn't check the Y axis), from the initial block. That means the command will checking the four corners of four different blocks (as shown in the attached image).
We can workaround this problem by either adding .00 at the end of the initial coordinates or using the execute alignΒ on all 3 axes.
This will cause a lot of issues for players who are new to commands, since most of the tutorials out there won't really use the decimal values or the execute align function.

Affects Version 1.20.20.22

Affects Version 1.20.20.23, Affects multiple platforms

Affects Version 1.20.30.20

Affects Version 1.20.30.21

Affects Version 1.20.30.22

Affects Version 1.20.30.24

Affects Version 1.20.40.20
Thank you for your report!
We're tracking this issue in https://report.bugs.mojang.com/servicedesk/customer/portal/2/MCPE-174949 , so this ticket is being resolved and linked as a duplicate.
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Can confirm been a bug for a while now