Most of this achievement shouldn't be an issue and if someone wants to provide a full solution for me to edit into this one or make their own, go for it.
But, the most likely to be a problem location is the sign next to a waterfall in the Primeval Grotto (Floodmore Basin) near one of the ancient writings:
https://clips.twitch.tv/TastyEnjoyableBasenjiAMPEnergyEdit: Some people have had issues where even though they did have every location, it did not work. These people have also had success in getting it in their TVHM mode once completing the requirements again.
"I've been going through getting these achievements, followed that theory that if you go to sanctuary, turn off revenge of the cartels and mayhem mode then save and quit they'll unlock if you visit all the locations in one go (making sure to not go back to sanctuary). Has worked a treat." - Punderstatement