...It's supposed to?? You wrote it...why should it feel like a totally different story just because you haven't seen it in 4 months? Do you forget that quickly when it comes to media written by other people (I sincerely hope not)...?
Like, obviously, it makes sense that some things might fade from your mind over time, like the specific words your characters use, or the implications of certain events. But your story should feel familiar and predictable when you re-read it. That's not a problem; it's an indication that your brain works correctly...
...Personally, I feel that if your story feels good to read when you come back to it, that's a good sign. ._. The idea that it should feel "worse" later and that if it doesn't you need to wait until it does...feels like a great way to teach yourself not to trust your own judgment and train yourself out of having confidence in your work.
I mean, I get the logic behind it-- sometimes it's hard to see glaring problems in the moment; something you thought was gold when you first wrote it can feel more like lead when you come back to edit. But in the grand scheme of things, your editing should be motivated by something besides just "ick factor".
Does the writing make sense? Does it serve a clear purpose, does it suit your style? These are the kinds of things you should think about while you re-read, so that when something feels "worse" you can actually figure out why, and when something doesn't feel "worse" you can still tell if it does or doesn't belong in the story regardless.
...That is some...strange logic there...
I don't know how you perceive your writing process, and I probably never will, but...IMO, this idea that your story should be constantly surprising you and immersing you in unanticipated puzzles and dilemmas...feels unrealistic.
Like, it feels like the way non-writers talk about writing-- like it's supposed to be this magical, transcendent experience, and if it doesn't feel that way you're doing something wrong and everyone will be able to tell.
Meanwhile, every vaguely experienced writer I've seen speak about their work, whether they're an amateur working on their first fanfic or a published professional...approaches it with a large degree of familiarity. They'll treat it like a pet, or a garden; something they gradually raise and cultivate and have a large degree of control over. They may have to tame it or prune it back occasionally, but they are in charge of what happens to it.
This idea that IT should be in charge and IT should automatically signal to you when something's wrong, and you shouldn't know where it's going or what it's doing once you take your eyes off it...is not common. Probably because it would indicate that it's not really your work anymore...a story that you as the author cannot predict or control is just brain vomit. A dream sequence in prose form. Which CAN happen, but most writers wouldn't consider that a 'story'.
All that is to say-- if you think about making an edit and you come back four months later and still think about making that same edit...and then you make the edit...congrats, you are a normal writer. 
I'd really like to know what could possibly be wrong with that scenario...
