I have an FXML file: main-view.fxml which functions perfectly fine, displaying eveything as expected when run within the project and showing zero errors in IntelliJ's FXML editor. However it is unable to be seen in intelliJ's built-in scene builder or in the standalone one. I've tested my other files and they all seem to be working as expected. I've also uninstalled and reinstalled the standalone scene builder.
I've searched around and I think there's a problem with the root Node or one of my imports but they're all the same as my other files. I've also gone through the entire file and haven't found an issue.
Link to FXML file in question: here (It's very long)
Thanks to the suggestion from @kleopatra I was able to find the problem:
It seems I had a closing <rowConstraints/> tag without an opening one that didn't impact functionality but caused the file to not open in Scene Builder.
Hopefully this will help those in a similar spot in the future.