The unstable crevice doesn't have a specific location it spawns randomly in Balenos, Serendia, Calpheon, and Kamasylvia regions.

Just sell the item because it is very hard to come across one.

If by any chance you came across one, you will put the honey jar and receive laila petal

Several of these spawn around Heidel(outside not inside city) and King's forest, sometimes several spawn at once They also spawn at night-time but they stay active despite it turning to day quite a while.