I'm embarrassed to admit this, but after downloading the complete BIAB Real Tracks again and reinstalling everything to no avail I was about to tear the rest of my hair out when I noticed (for the first time, obviously) those little pictures with names under them, including RealTrks.

I swear I've never noticed them before, and definitely never clicked them.

On clicking, I found Real Tracks Preferences, where High Quality Pitch changing AND Use 4 bar endings for Real Tracks were UNSELECTED!!!

I selected them, rebooted the program and Viola! the endings were back to normal.
How I missed this I really don't know, (and I don't know how they ever became unselected) but it's now fixed, so thank you everybody who tried to help me and apologies for wasting your valuable time...

Whoo hoo I'm so happy!!! :-)