Hello Sami,
Until now I hadn't tried to use an old (pre-AU3) VSL multiport template with VEPro7, but your plea for help spurred me to do some testing. Previously I had no problems using those templates with VEP6. Well, you're doing better than me with VEP7: testing the old VSL 6x16 Logic template with VEP7 I can't even find where any MIDI is being delivered in instances 2 through 6 .... ei saatana! (Sorry but In Finnish I know only how to curse, although I'm trying to be somewhat polite for the VSL forum, lol.)
It does seem something is very wrong somewhere but I'm still investigating. Thus far, I have MIDI communication working as expected only for VEP7 instance 1. When I try to play MIDI notes to a different instance, the MIDI indicator lights up in the correct instance tab in VEP but does not appear to be delivered to any of the 16 MIDI channels in any of the first 16 ports in the instance (perkele!!).
I'm currently using VEP 7.0.926 with LPX 10.4.8 in MacOS 10.13.6 on a 2017 5K iMac. What version of LPX are you using, Sami? I still have a copy of LPX 10.3.3 and I'm wondering if that might behave more like your version.
Apple have been tinkering here and there in recent versions of Logic's Environment, and I do NOT trust their tinkering in that particular area - for example, they've broken a certain function that I relied upon in the Transformer object and it hasn't been fixed in the last 4 Logic updates. If we can precisely pinpoint and define fault conditions in the old multiport operation with VEP7 then at least we can send sensible bug reports to both Apple and VSL.
Sorry this post is not exactly helpful; I'm continuing to investigate as far as I can.