User blog comment:BannedLagiacrus/Discussion of the Week: Hidden Remains/@comment-36756441-20190110213214/@comment-8897944-20190111065945

It didn't return because the team couldn't make it work correctly in MHGen due to time restraints (it crashes MHGen somehow) and Volcanic Hollow is basically Sunken Hollow but has awakened due to 4 and 4U incidents. So, this reason has nothing to do with its absence in MHGen. It can also appear in Primal Forest which further invalidizes the reason. It can easily go back to Primal Forest but we don't see it in MHGen at all. Why? Because it's not available to hunt. They finally managed to fix its crash issue and that's why we saw it in XX again.