Blueprint functions appear to correctly associate local variables when renaming the function. However when undoing a rename with ctrl-z the local variables appear to lose their association. Redoing after undoing appears to fix the issue.
This was reported and testing in 4.24.3 (CL-11590370). This was reproduced in 4.25.3 (CL-13942748), and 4.26 Preview 2 (CL-14419252)
Results: Warnings will appear for each instance of the local variables use in the graph.
Expected: successfully compile.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-100788 in the post.