Very specific & peculiar behaviour but I encountered it yesterday & figured out a fix for it today (which would’ve saved me time yesterday!) so I’m sharing it here:
For some reason, when copying some math modifiers and envelope modifiers between layers and between projects the modifiers would carry over their values into their pasted locations but wouldn’t “function” as expected - the math modifiers still had their values for the modifications they were supposed to perform, but their targets weren’t changing at all when I pressed play. When I tried to recreate this in a simplified form in a new project file for a bug report, I closed the project file with the issue. When I was unable to recreate the issue in a new showfile, I then re-opened the project file with the issue and found the copied nodes were now functioning as expected.
I don’t really know how to provide a DFX file that recreates this behaviour beyond sending the current project file with instructions to copy & paste some math modifiers into a new layer. But maybe this might be helpful to someone?