I believe I only had major shifts when I was more immature. Back then I was more prone to bias and was more reactionary. I also learned the importance of informing myself properly on a particular issue, especially if reflection alone couldn't give me sufficient answers.
I remember having some big swings in my opinions towards the Israeli-Palestinian conflict in my late teens to early 20s. Then a few things made me feel I should learn more about it. I ended up reading about a dozen books on it and realised how stupid my previous judgements were once I saw the complexities of the issues/history involved. Still, my values hadn't really changed much (even in the big shifts), it was just how I applied them.