Hi 99.99,
I don't know if this is relevant but I had a similar experience when looking for the thread on "Predestination, Free Will and Astrology", started by Trois-Rivieres - all of that individuals posts have gone, it seems.
I have copies of all my contributions so, in principle, I could reconstruct that thread by referring to the original stimulus (an internet article), then adding my views, perhaps in edited form.
However, it may be that there is a specific reason those threads have disappeared. I'll wait and see what is said on the matter.
Henry.