Just after the festival started I went and did trick or treating as much as I could before bed.
Then in the morning(7+ hours later) I tried to do more, but everyone I try to trick or treat gets the message 'This Player still has an open request from you!' and has 'You can Trick or Treat a Player once every 6 hours.' under their trick or treat button(not sure if it is supposed to be there)

I went to work, and ~10 hours later(now ~9 hours after the initial bout), I still cannot trick or treat anywhere.

Note: I am able to hand out candy and items, and collect candy from my basket, but not knock on additional doors.

If the person you visited never answers their door, then your visit will just sit there until they do. And while that visit is open, you can't open another one with that same person.

And there's also a 6 hour cooldown between visiting each player. So if you visit someone and they answer, you have to wait at least 6 hours from when you visited them in order to visit them again.

If you use the green arrow buttons, it should only cycle to valid players for you to visit. It should skip over all inactive players and any player that has an open visit with you already.

I am primarily using the green arrows to navigate and cannot seem to find any doors I can knock on even though it has now been > 20 hours since my last successful attempt to knock.

Unless I am misinterpreting the 'you have now submitted this one, move on' message as 'nope, can't submit because you already did'...

You don't seem to think there is anything strange in what I am seeing, so I'll just assume I was misinterpreting it until I see evidence otherwise.

Sorry for the bother.

If the issue still appears, take some screen shots and post. :O

There are three players that will always appear when you try trick or treating.
1.) Krinadon (because he's the first player ID- this just lets you know you've reached the very first door)
2.) You (Because you have to have access to you!)
3.) Last player ID# (ID# represents the very last door or end of the line)

If those are the three cycle through options you get, that's normal. :)
More options will appear again when they're available.

That doesn't sound like what's happening though?
Have you attempted to use a different browser?

No worries. Posting issues is what this forum is for. =)

Sometimes it's hard to interpret player experience's through text alone. As Imperium suggested, if you're still having an issue, try taking some screenshots so I can see exactly what you're seeing.