The site suddenly started having a lot of 502 errors while I was doing Major Drills quests. It just froze every time I tried to complete one of my last quests. This happened even when I went round the site looking at restocking shops before trying to use the complete quest option. When it finally registered I was told I'd done 32/30 quests and had a few prizes which didn't belong to me. I've now deleted them all.

I had the same issue today. I hit a wall of 504s when trying to finish quest number 27, refreshed a few times (stupidly), gave up on trying and then a few minutes later I saw 33/30 completed Drills' quests in the quest widget and found some extra items in my inventory. I deleted the items.