I read yours too and this was definitely something I noticed (read it without checking the other feedback first). I was even a little more confused because on the cover the vending machine was in space, so I was wondering if we were kind of time/space shifting in an area around a magical vending machine.
I don't think you need to draw a background on every panel, but you could use a very desaturated/just a few sketch lines to suggest that the characters a not in a void or grab pieces from the establishing bg you already drew? You can fade/desaturate/blur them so they don't compete with your characters. I really loved the lighting you added that illuminated the sidewalk a bit that you did in some of the panels.
Though that was somewhat confusing, I think the choice to use the 4 long horizontal panels on every page gave me the most trouble. There's pacing, flow and focus that I think would greatly improve your comic if you opened up that structure. As it is it will feel like everything is happening at the same speed and the reader needs to do the mental work to understand if you are showing us moment to moment or a slower sequence, for example. Plus you will be restricted in how you can crop which I think exacerbated the feeling of a void.
Whew, as the focus of the thread is the criticism part I feel like this was tilted very negative so I've just got to say your artwork - lines, anatomy, expressions - looks really great! I absolutely love the environment you drew behind the vending machine and think you should find sneaky ways to keep using it. And the pets... Omg so cute!

I find that the negative parts of criticism are extrememly helpful and sometimes people are shy about giving them. Have at it!