I think they mean, not that there are multiple organisms in a photo, but that they are seeing species complexes of similar-looking, but distinct and described species, all being labeled as one species on iNaturalist. I’m not really up on moth species complexes, but for example in my area there are 3 Lithobates frog species that look quite similar. Despite the difficulty, people do try to correctly identify which one it is, and the CV has all three options as suggestions in the appropriate area. I think they are describing a situation where instead of separating multiple species into their appropriate species designation, people are picking one species consistently (likely because the CV only has one species, and continues to get trained on multiple species as one species).
I mean, if you have the time to spare and the expertise, being the person to sort out those species complexes will begin to correct the problem because the CV will get trained on providing those multiple options and people who default to the CV options will be able to see there are multiple options. You can also flag the pages for the species that is being assigned to bump the issue to the curators and see if they can help you sort it out. While new observations come pouring in, it might be good to add your ID as the genus/higher level classification that includes the described species and have a copy+paste boilerplate message at hand saying something to the effect of “this could be species A, species B, or species C” so people aren’t confused why you are bumping it back up from species. I think a lot of tropical species have this issue.
I’m not a mod/iNaturalist employee and I’m not sure what the official recommendation is here, but it does seem reasonable to clean up what you can. For example, see this thread: https://forum.inaturalist.org/t/harebell-help-needed/53414