Hi Daniel,
I have to admit I was wrong!!!
I followed your advice, plus bought a new SSD disk and proceeded with a Omsi fresh install with it.
Starting with the basics, only the Omsi core game plus BBS-ON, AUXI tools and Enhanced Environment Pack, BOTH work without any issues.
So I apologize for inconveniencing you and wasting your time in order to resolve an issue that was clearly my responsibility!
I think I should close the issue as a resolution of my own fault.
I hope my "good luck" continues tomorrow when I install and everything else.
Thanks and sorry again!