Hanging vine bug

Herugrim

when I found some hanging vines in the kelp forest (the purple jellyfish looking things) I was unable to swim between them like I used to. An invisible wall stopped me and sapped my health. Blocked off an entire cave system that had sandstone deposits I was completely unable to reach.

Rainstorm

I think youre referring to the drooping stinger plants. Yeah, i hate those things with a passion
Technically those plants arent supposed to have a collision so bad that they prevent you to go thru them. Doing so will result in massive damage but you should be able to pass thru it nonetheless.

that definitely look like a bug and if you could post a screenshot here with the F1 window up (so that the devs can see its exact location) that could help them ID the faulty plants better