I remember this bug happening awhile back, but couldn't find a report for it, so here's one:

Description of the Bug: So I was doing the Diamond Nugget quest again, was severely under-leveled to fight the level 42 "Sunobra" and lost. Now the dialog option to start the quest is unavailable despite multiple explorations.

Steps to reproduce:
1. Start the quest by exploring at the Mana Stone Mines until you're given the option to "Look for our good friend, Zavier." and start the quest
2. Fight the Sunobra and lose or flee
3 Return and explore at the Mana Stone Mines for awhile

What should have happened? Normally after losing a fight, you can just come back and do the quest from the beginning again

What did happen? Explored for a few days and found nothing

My System: Win 11 PC, Firefox 136.0.1 (64-bit)
Affected Pixpet: Pentest Dragon

You explore at [Block ID: 1751] until you get [Block ID: 2509], which gives you the option to "Look for our good friend, Zavier."
The very beginning of the quest starts on [Block ID: 2510]
Right before the Sunobra fight is [Block ID: 2519]

Interestingly enough, when you come across a quest like this and choose to Return, an dialog option will pop up where you were exploring to continue the quest. Here and on the scroll quest, however, you have to explicitly explore to get the option again. Don't know if that has any effect on anything.

Bonus bug: The Sunobra you fight is actually a Nightshade Sunobra