No "open panel editor" button

You could try this:

- Close (completely quit) the Panels client
- Find where your panel is saved - mine is in C:\Users\youruserprofile\AppData\Local\Packages\14495Panels.Panels-CustomUIBuilder_t203xt8whertw\LocalCache\Roaming\PanelsApp\panels\mypanel
- Open the folder for your panel and you should see a file named Settings.json
- Open the file with Notepad or another text editor
- Find the end of the text and you'll see a key that says "PanelEditor":false or "PanelEditor":true
- If yours says "PanelEditor":false then change it to true
- Open Panels client and hopefully your panel can now be edited

If this works then great, otherwise I'm not sure what would cause this I'm afraid, I'm not an expert panel creator or anything, just trying to lend a hand
Good luck!