Somehow the problems seems to be solved.

Could because of a reboot.
Could be because of the latest update patch. Probably. It was a big one.
Could be I did something wrong.

I can generate now without crash.
The RT does not change anymore.

One small thing left.
All RT are now marked as N/A in Reaper BIAB plugin. (They are fine in the real BIAB) But I can hear them, mute, sole and change volume. So it is a small problem.

If I double click on this N/A RT instrument I get a menu "Assign Real Tracks to track" with only two rows: <NONE> (Song doesn't overwrite RealTracks) and <SILENCE>.
Once again, I can hear the track so it does find the sound file.

RD are fine. It sounds good and no N/A.