I came across a post on r/ableton in Reddit about a bug which a user encountered whilst using the Max For Live Envelope audio effect.

The original post highlighting the issue linked below.

https://www.reddit.com/r/ableton/comments/9vcc51/the_m4l_envelope_device_is_broken_can_someone_fix/

The bug causes the envelope to trigger twice whenever a 3 note chord is played, strangely 2 and 4 notes do not seem to exhibit this issue.

After a quick poke around within the patch I found that inserting a [change] object before [sel 0] has eliminated this issue.

I have reported this bug but in the mean time, I advise any Max 8 owners to modify the Envelope Max For Live patch directly (screen shot below for where to place the change object) or if you prefer, you can download modified patches (for ableton. v9 or 10) linked below.