Just an update: this issue also translates to Synth, and it’s been logged as such here Mod Matrix Destinations Related to Envelopes Don't Work
I will link it here for transparency and updated the title so it reflects the issue better.
We’ll have an update for you as soon as it’s resolved. We appreciate your patience while we work on it.
The bug template probably wasn’t designed with this scenario in mind, but I think when you merge bug reports for several devices it’s a good idea to list all affected devices and their firmware version in the description.
For this bug it should probably say something like this:
@Lizard-of-Oz You’re absolutely right — the current bug template doesn’t fully account for scenarios involving multiple devices. (@Sandroid FYI). Feel free to edit the post above and I appreciate you taking the time to point this out. Internally we track it across all affected products. Cheers
I’ll see what i can do to update the submission form 
Very nice catch @Lizard-of-Oz! 
Any news on when we might expect a fix for this? It’s been over a year since first reported. Is it in active development? If this modulation works correctly on the Tracker + it would seem the solution is already known though this could be due to an architectural difference between the Play and Tracker.