What is with this crap rate company already. No matter how many times complete earthcrawl mines on tier 4 or higher it never shows completed on this achieve.
Looking at the topics everywhere, including the WoWHead comments, looks like it is a bug. Possible that it was not intended to be open at launch and will likely finally pop when either 11.1 goes live, or Season 2 hits.
I got the achieve without issue (I also have the rank 3 achieve). Not sure why it isn’t working for others. According to wowhead, 20% of accounts linked also have it.
Most likely a bug keeping you from getting it. I’ve got Delve Deeper thru Delve Deeper III done and progress toward IV but not really making it a point to get that one done yet. Toss it in the bug forum and see if one of those folks can help you out. One managed to unstick one of my DHs that was broken since early BfA lol.
The only suggestion they gave was to create at least 10 more characters and classes and try on all of them but it is working as intended?!
It is actually an odd bug they have not documented well. It will complete as soon as you get all of the other delves done on tier 4 or higher. For some reason it will not register Earthcrawler Mines until last even if you do it first.