I’ve made a ticket in game for this already, but so far I haven’t gotten anywhere with it so I thought I’d make a post about it here. In Remix I’ve been doing all of the Touring achievements to get the rewards for them. These always include exploring the zone you’re in to contribute to the bigger achievement. All of the other ones I’ve done haven’t given me issues until now with Explore Dread Wastes. I’ve explored the entire map but one area remains greyed out; The Clutches of Shek’zeer. I’ve flown over the area for minutes at a time trying to get it to pop and gone to exact coordinates to no avail. I’ve tried turning off addons and reloading, relogging, and restarting my computer. Nothing has worked. Unless I’m missing something so miniscule that it’s not giving it to me, I have no idea, but I’m assuming this is a newer bug since I haven’t seen much about this anywhere else. It’s actively preventing me from completing the Touring achievement for that zone and I’m missing out on the rewards from it.
Oh, hey! Someone else with this problem!
For me it’s the same zone (Dread Wastes) but it’s a different sub-zone (Kypari Vor). Interestingly, it gave me the original version of the Explore Dread Wastes Achievement but not the Remix version, which is I suspect the cause of the problem; the game checks to see if you’ve been given credit for exploring that sub-zone, and since you have, doesn’t bother looking to update any relevant achievements. As for why it skipped the remix one I can’t say, but it is annoying to be permanently blocked from this achievement.
And, though I still encourage you to try, GMs can’t help you. Filed a ticked and got several responses, most of which read like canned responses, but the last one actually seemed to understand and told me…to post a bug report.
So, bumping for visibility, but we’re probably perma stuck.
That’s really unfortunate 
I wonder if trying it on a different character would work? I’ll have to take a look at that and report back here. This bug seems newer since the only other post I’ve seen about it was yours so I don’t have high hopes for help.
I just completed the achievement on an alt! I was able to explore the missing area on my level 14 I had without any issues. Try it on a lower level character and see if that’ll help.
I will also note that I still cannot complete the Touring achievement for the area on the main character since the achievement isn’t working on them. Maybe because I started the campaign quests there on him? I’ll have to do it on that alt now but it’s good to know that it’s not totally locked out forever.
Indeed. This seems to only happen to specific characters, most others are fine. I was also able to do it on an alt (and with one more rare, I’ll be able to finish the Tour achievement as well). It’s just unfortunate that I can’t 100% the remix achievements with one character like I (and I suspect Clertirolex) was trying to.
I am having the same issue with Explore Krasarang Wilds achievement. I cannot get credit for The Deepwilds portion of the achievement even though I’ve been in that part of the zone multiple times.
It looks like other people on WoWhead are also having similar issues with other zones.
This quest was not working as intended for my Mists of Pandaria: Remix character on Area 52. The smaller mantid were available, but the three larger spawns were not appearing. I tried logging out and back in, leaving the zone and reentering…I even waited for about an hour…nothing. Here’s the workaround I used to complete the quest. I used a newly created MoP: Remix toon on a low-pop role-playing realm (Argent Dawn in my case) to invite me to their realm. Once there, the three larger spawns were occurring regularly, and I was able to complete the quest easily.
Several of these Explore achievements are very finicky about just what pixel they want you to stand on. A good example of this problem is the quest you pick up from Kairoz on the Timeless Isle. To get credit for Firewalker Ruins, you need to go over the ramp (not up) to where the cranes are and get in the sea against the cliff.
With some of the Achievements, I suspect part of the issue is phasing. That is, some unknowable area id only rotates into your view when you have completed some quest or another.
Currently dealing with this as well. Had unlocked almost all areas, flew by Dak the Breaker, dropped down to kill him and as he came off his stone I d/c’d. I logged back in and I was on the complete opposite side of the zone, with a whole bunch of areas that I needed to unlock, not just the one I had left. My entire map was uncovered though. I have yet to be able to actually unlock any areas as… they’re already unlocked.