Fascinating, Cyril.
So the performance of Logic's Environment is completely independent of any design and build of Logic; any design and build of the host computer hardware; and any design and build of the host's operating system?
In other words, Logic's Environment is some sort of ... erm ... transcendental thing?
Truly fascinating.
Ahem. Meanwhile, I'll just carry on in my mundane world with actual software and hardware. And since Cyril asked me so nicely, I've attached below a screenshot. The inserted Monitor object is displaying spurious Note Off events after a single C4 1/16th note - created in Logic's MIDI region editor - is played back through Port 5 of a copy of VSL's 1x16 Ports VEPro/AUv2 template.
I'll spare readers the tedium of me posting other, more elaborate test results I've obtained. For those I've connected this VSL template (with and without Cyril's Monitor insertion) to an External Instrument plugin routed to an external IAC Bus monitor. Suffice to say the Environment in Logic 10.7+ seems to have adopted a ... uh .... 'new and different' way of performing transcendentally! Lol. Seriously though, it gets quite spectacular over time when several different notes are played back.
Given the nature of this egregiously aberrant behaviour in Logic 10.7+, I seriously doubt there's any chance of a user-level workaround in the Environment for this problem. In my book it's definitely a dev job for Apple. Until then, alas, it appears there is no way of using Logic 10.7+ properly with either the AU2 or AU3 version of VEP7.
Moreover, although I haven't yet had time to characterise it more definitely, there is strange behaviour in the Environment of Logic 10.6+, as I've already noted in a post above. As far as I've seen, this particular strange behaviour is not present in 10.7+. So for now I won't recommend 10.6+ for users of the Environment. I can recommend 10.4.8; it works fine with my AU3 template along with the very large and complex design that I have in my Environment.