That last part seems rather unbelievable between good friends. Have you seen something like that happening to someone? I cant imagine this happening with my friends since I only have few but close friends.
I also really hope my suggestions are just bullshit. Especially since those have the worst implications. But I would still be watching out for similar events. Just in case :)
I am not sure if this is a joke. Most commentators seem to perceive it this way. But just in case I will answer seriously.
This was done by a human:
your kid (you said you live alone, so not this one)
your guests
someone uninvited (but it makes no sense for them to leave this)
you in a way you cannot remember.
I will expand on that last one since no one has done it:
Do you have an issue with substance abuse?
Do you have issues with your memory?
Do you have any psychiatric issues? Your other personality could to this if you have a dissociative identity disorder. Check symptoms and pay attention on similar events.
If this keeps happening go see a doctor.
Nope. Most tracking is not happening based on an IP address, which VPN promise to hide. But rather tracking what websites are you visiting (that run a common tracking code and sending those data to google and similat) and yhen linkingball of that to your identity on websites you are logged in...
Or drinking directly out of the cabinet?