Wait, if they were forgetting that they were writing the notes, why did the handwriting look like the landlord's and not their own?
This reminds me of something similar that I experienced.
When I was younger my mother and I started noticing food missing in that there would be less of a bag of chips than we recalled. Nothing was ever completely eaten and the food had to have been opened first. We were pretty sure something weird was happening, and then one day we got home and I noticed there was a can of pop missing. I was absolutely certain I knew how many were left, so at this point we were convinced someone other than ourselves was responsible. After talking to other residents in the townhouse complex we find out we're not the only ones that this is happening to.
Fast forward a few days and I'm locked out of our townhouse. I went to my friend, who lived a few townhouses down, and asked if I could hang out for a bit as I was locked out. He proceeds to tell me that the caretaker's daughter who lives in one of the townhouses has a master key and can let me in, as she did it for him before.
We walk over to her place and he asks her to let me in with her master key. I will never forget the mix of anger and fear in her face as she weakly tries to deny having the key, only for him to bring up past incidents she has let him in. She relents and walks us over to my townhouse and lets me inside.
Amazingly, after that day we no longer had food and pop go missing.