Hi @PeterKHewer, pleased to hear Scaler v3.1.2 is working well for you, however the issue you are referring to where Scaler 3 standalone quickly closes after opening is usually on account of a corrupted standalone state file. If this ever occurs again it can likely be resolved by deleting the standalone state file.
You can find Mac and Windows instructions for this at the bottom of the Known Issues forum page.
I will excerpt you remarks and put it in a how-to or other help directory for Scaler. For your info, in the past for Scaler 3.1 and 3.1.1 I did several things probably including what you are saying is the solution but nothing fixed the problem.