When volume target selectors(like @a[x=5,dx=99]) are used, they dont select entities that have different coordinates than you defined(if you define x, y and z must be the same as the command block)

Steps to reproduce:

1. Place a command block down very close to 0,0.  You have to so the command block is loaded when you test the command. You can do it somewhere else if you change the command accordingly.

2. Put the command block in repeat always active mode.

3. Put the command "tell @a[x=5,dx=99] testing" in (without the quotes)

4. Notice when the command block spams the chat.

What I expected to happen: The chat would be spammed when my x was between 5 and 104

What happens: the chat spams when my x is between 5 and 104 and my y and z are the same as the command block's y and z.