I've also had problems, and the following solution may help others.
When I know I've contributed to a thread I call up my list of postings (click on my own name at the start of one of my recent postings)
These come in lists of 200 at a time, running back from the present. I then use the "search this page" function (Under "Edit" on toolbar) to search for a word or phrase which would have been in the thread title.

Nigel