The Mechagon meta-achievement requires two items from doing the hard mode reclamation rig event, which will be difficult enough on it’s own to activate given that people overpower it, but the event is frequently stuck (today at 97% progress) with no further advancement possible.
FWIW I think all of it is buggy. Last time I tried to do the Reclamation event in Mechagon was towards the end of patch 10.2.6 and I was the only player nearby. Upon completing the donation portion to start it up, it immediately de-spawned…
I had progressed it from 0% to 100% all by myself using mats I’d held onto since Battle for Azeroth was current, too. 
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Oh no! I’m sorry to hear that. I had been doing them without issue for a short time as I only started working on the meta recently, but noticed the last few times it’s up it’s been stuck. 
I usually find it that way so I don’t get a chance to see if anything in particular could have triggered it.