If you do a standard PhpStorm/IntelliJ search Ctrl+F, you will see instances represented by yellow "notches" on the right hand side scroll bar:
but when I do the same search using IdeaVim's search /, I don't get the yellow notches:
Thank you in advance!
Check that the Search Results | Text search result colour option has the Error stripe mark value checked. IdeaVim uses this to show the stripe on the scroll bar, and doesn't show anything on the scroll bar if it's unchecked.
However, the standard Ctrl+F find results will "fall back" to creating error stripes with the background colour.
I've raised an issue (VIM-1773) to get the same behaviour in IdeaVim.