hi, I thought I'd make a quick post regarding this issue, as I'm experiencing it as well and can't seem to solve it after repeating the steps you had mentioned to the previous user.
Here's a screenshot of the issue itself, and my gamedata folder. https://imgur.com/a/coDILzi
The only other possible solution I may consider is to reinstall waterfall itself but other plumes on non-srb's work fine, so I doubt that's the issue.