Sorry that I didn't have enough info captured to help diagnose properly. As I indicated in previous message, the machine is in production now so I can't break it for testing any further. Additionally I know from previous breaks, it will corrupt all HDD contents (full reinstall from scratch) which I'm not in a position to do either.
So, this topic must be closed I think, and maybe if someone else has similar problem in future they will find this thread and proceed appropriately.