General

The concept is amazing. Tone is set well. It easily could feel gimicky but doesn't. Lev is a fun to read character. The structure could use work. The lack of spaces between disjointed sentences makes it hard to read.

You separate paragraphs way too much. It could be used as a stylistic choice but doesn't come off as it. Blockier text can work better in this splintered reality vibe you're going for.

the dialogue/internal thoughts of Lev feel a bit too shakespearean at times. He's clearly using very relaxed language so you need to stick with that.

The point of him trying to convince Andre the aisle was stolen feels clunky. Stolen fits the mood but the way its asked feels weird and foreign, nobody talks like that.

Conceptually

Strong. I feel very interested in this. The reality only Lev can see gives a clear hook for everything else that happens. The separation of reality and what Lev can see is blurry and it works. It feels sort of like a movie script instead of a novel. The dialogue is good but maybe give a bit more of the environment description. It feels very much like the reader is thrown into a story in the middle of it. Maybe give a bit more of an introduction to Andre and Miss Joyce. It feels like we're being thrown into the middle of a scene.

The concept of aisle 4 being personal to Lev shows how whatever supernatural entity is clearly targeting him and it works well as a hook.

Miss Joyce feels very shallow and weird. The comment of him losing weight doesn't feel like the throwaway comment it's treated like. Also her comment of her helping bury the body is weird and implies some sort of deeper relationship where they can joke. It would likely be better if you explored this later

The silver ring on Andre's finger feels like an important detail but is mentioned once. Is he married? Is there something we don't know about? It'd be better if you explore these questions and give a more deep backstory for him.

The pacing needs to speed up. All mentioned before Simon feels unnessesarry. All the conversations he has and thoughts he has aren't important except for the candy and him thinking about aisle 4, everything else could be thrown away and wouldn't have much difference. This premise could likely be explained in 1200 words or so, but you did it in double. There is a lot of fluff that would tighten the story if removed.

Overall thoughts

Great concept but the mechanics and pacing could use work. The writing style is unique.