Nostalrius Begins - Quality wow vanilla realm (1.12)

Is there any records of people losing quests out of their quest log?

I was in Darkshore questing when one of my quests disappeared from my log. I returned to the quest giver, but he did not have the quest for me. I shrugged it off and continued.

Now I've recently lost the deadmines chain quest and can't acquire it again through any means I can find.

I'm concerned this may cause issues for me later in the game for attunement quests and long chains.

I have not experienced anything like this, but my advice to you:
gather more details, like server time when it happened, quest name (if it is possible), what have you done during the time of acquisition and the time that you seen the quest was lost, any other details that could be relevant and create a post here or got to http://report.nostalrius.org/plugins/tracker/?tracker=14 and create a report file there.