When using commands with target selectors (@a, @e, etc), players can add additional parameters inside of square brackets. These include but are not limited to count, coords, and tag. You can list multiple of these parameters together as long as they were all inside the brackets and separated by commas. In 1.13, it's been limited to just a single parameter. To be clear, this is not working as intended, because since these parameters were added to the game. all previous updates allowed multiple of them at once