I think I have exhausted all the options. Unfortunately it means a fairly big change to my code as this cluster indicator is used repeatedly. It looks like this has been a bug in LabVIEW for at least the last 7 years, surely it is worth fixing?
EDIT: By switching off defer panel updates I can now get the graph to update with the method above albeit with missing information. I believe waveform charts in clusters only update given certain conditions relating to detecting value changes. Looking at the information displayed compared to that of the same waveform chart wired directly, it is not a good representation of the data and I will still be redesigning the code.