I was tracking many threads and they all just disappeared.

That is likely due to the fact that you tracked these all at a similar (ish) time, and the time frame for how long you chose to track them went out/ was passed. Upon tracking topics you can decide for how long you'd like to track them, and you need to renew that before it runs out.

nah several were tracked today and others were all various days. every single one would not have expired at the same time. i had a couple marked for a year