There have been a couple of threads on this. The workaround is to "bookmark" the trainer history so you can get back to it. You could do a forum search and the archives have the original threads if you want.
Where's my tactics trainer history?
I looked for the threads you mentioned, but didn't find anything. As of Tuesday the 26th, that problem has gone away. Now when I click on Tactics Trainer, it brings me to the stats page, with the history of my puzzles.
Now there's a new problem. Everything Tactics Trainer related seems to bring me to that same page. Clicking on a puzzle in my history brings me to... the stats page. There's a new comment on a Tactics Trainer puzzle? Clicking the link from my home page brings me to.... the stats page.
Seriously...
This is written on Sunday, November 24th, 2012.
When I logged on this morning and clicked over to tactics trainer, I notice the first puzzle loaded immediately, and a new window opened on top of it, telling me my rating and asking something about if I wanted to practice? When I agreed, I played my 3 daily puzzles. I wanted to go back and review one of them in a little more depth, but now when I click Tactics Trainer it brings me right to the screen telling me to buy a premium membership if I want unlimited puzzles. That's not what I want, I just want to see the history of the problems I've done.
Anyone else having the same problem?