This morning I tested a package for the compatibility modes Windows-Legacy, Windows and Cross-platform. I builded the same workflow for each test case. For the return value I use a variable with the name Return. It works in Windows-Legacy and Windows compatibility mode, but not in Cross-platform mode. Here I got the following error message:
It seems that Return is a reserved word in this context. Not a great problem, but interesting to know, because if you want to use workflows across compatibility modes, the variable names should be chosen correctly, not reserved words.
You can find a list of the reserved words for VBdotNET here.