2001 Nissan altima timing issue

Ok so I was having a serious problem with my car not accelerating properly. I woyld be floor I it and wouldnt go anywhere. I got frustrated after numerous tests and trying to figure out what was wrong so I took it in. Turns out the timing was off twelve degrees. Once it was fixed it ran beautiful. I took a two hour trip and when I came back home I noticed it was starting to feel like its jerking and taking a while to accelerate again. I know for a fact that it is a timing chain. How can the timing be off again? Unless its skipping a tooth or link on the chain. What could be wrong and what should I do?

might have a guide or chain rail or tensioner wearing out or bad thats allowing the chain to move to far and change the timing