References not highlighting all instances of the variable Follow

Hello,

The references in my plugin have stopped working as expected after one of the new releases of Intellij. When I place the caret on a reference, I would expect all the instances of that variable to be automatically highlighted, but instead only the one element is highlighted:

However, if I place the caret on the declaration of the variable, then all the references to it are highlighted (which is correct):

This highlighting functionality is very useful for my language, especially since it allows you to see all the instances of that variable along the scroll bar on the right, such as with Java:

I've tried debugging this and I've confirmed that all the right PSI elements are being returned by resolve() and isReferenceTo(), so I'm not sure how to fix this.

Thank you