This is already fixed by Jules on develop. It’s actually a compiler bug. See this github pull request for information:
Bug in juce_AudioProcessor.cpp (v5.02)
Juce 5, Visual Studio 2015 Incompatible?
ah, cool. funnily enough when I saw the problem I was quite flumoxed so added some braces to see what effect that would have and it fixed it - at least now I know why