I guess 
All BP nodes get hint : Call unknown function “function name”
Interestingly, the problem appeared in all projects using a certain plugin (VaRest).
And what’s even more interesting. If you manually recreate the structure. (I will call a few functions) it works in the editor perfectly.
However, after rebooting the editor, or trying to package the project for distribution. Again, everywhere is red.
After I read this post, I doubt that the bug itself would be caused by the plugin itself