Hey Chris,
I might be able to shed some light here.
The issue primarily arises from a conflicted definition of cleanliness. What you may be acustomed to may come as a shock to a guest. As a guest, I can tell you I have ran into my fair share of near deal-breakers, from exposed dryrot in the doorframes to early signs of mold in the bathroom ceilings. Although my examples are incredibly extreme, your guests are probably catching things you and your cleaner are overseeing.
The only way to be sure is to reach out to as many guests as possible and ask for honest feedback. A few of my hosts have left notecards to fill out about guest stays that stay off Airbnb's platform. You can set up a similar feedback system to collect suggestions after each guest stay.
"Hi, my name is Chris and I am leaving this note for you to fill in any suggestions you have about my place. I want to improve the quality of my unit for my future guests, so your input really matters. What can I do to make my place the best place possible?"
Also, some guests might be finicky about "cleanliness" or just looking for any excuse to vent about a horrible stay which you had no hand in. I work in real estate, and the negative comments people leave on our social platforms are hilariously inaccurate and clearly malicious.
The only way to combat the fake or malicious reviews is to make sure all your rational, happy guests leave honest and positive reviews.