Same for a gas tanks as I've just found.
Can't put a certain numbers since some tanks are installed on cars (and their volume rounded up) and some are dismantled from. So, what I have now for the "Standart small gas tank":
75% - 37.05
76% - 37.44
82% - 31
83% - 32
88% - 34
100% - 39
Just like the trunk volume, the gas tank volume seem like have a huge volume drop-down at about 80%
No problem. Triangles at doors too and luminescent wall vines.
I have no idea what's causing it, it used to just be on Erosion vines (was a consistent issue) but now it seems to be everywhere. You described it much better than me though.