I see this is a common issue so just reporting & asking for delete.  I've tried a couple of different ways, nothing seems to work.
Master tier subscription so I'm not concerned about immediate removal but if someone in support could please delete:
https://www.dndbeyond.com/encounters/50052e63-4b23-441c-bb4a-f569fb8eadea

Thanks!

Make sure that:

1. The encounter has a name.
2. That it is assigned to a specific campaign.

I built these earlier before I started getting settled in, learning how to work with the site so they're not assigned to a campaign.

I looked but was unable to find where that option is..?  (I have others created sans campaign that I did not make the effort to delete yet.)

Also, it seems opening the encounter, once inside, it has no name, no monsters.  Assigning a name creates a copy with that name which can be deleted but the original remains.

Quote from ReefJunkie >>

I built these earlier before I started getting settled in, learning how to work with the site so they're not assigned to a campaign.

 
You do it here:

Quote from IamSposta >>

Quote from ReefJunkie >>

I built these earlier before I started getting settled in, learning how to work with the site so they're not assigned to a campaign.

 
You do it here:

 Thank you very much! - I still can't delete the 1 problematic encounter but this should help significantly going forward.

I have this problem as well. I have 2 encounters I've tried to delete for ages and it won't let me. They have names, but when I click "edit" it forces a "new" encounter and not the old one.

You should both submit support tickets then. Be patient, it could take 3ish weeks or so for them to get to your tickets.