I remember this happening to me as well on my first trip to the Dregs dungeon, which is where i assume you are referring to,the place where you learn the blue glowing torch. I haven’t been back to see if its still glitched as i collect my glowing goo from the little passage way to Dagon’s Eye Temple
It’s not just the dregs. Over by a small encampment south of deathspire ruins and north of scavenges berth. in the water there is supposed to be a plant as well. And it is invisible also.