Right after I graduated by BSc degree in Chemistry, I joined the group of a professor as a research-assistant who was willing to work with me for a few publications before I could be admitted since I only had a second-lower honours degree. Long story short, I worked there for two years, and at the end of that, I had a episode of mental breakdown where I needed to be hospitalised. With all the stigma surrounding mental health,my PI just didn't believe me, saying "I don't think your problem is that important", and "you may take leave if you want since it is your right, but there will be consequences to this". I ended up leaving, did a Masters degree, and am now trying to look for PhD positions.
I am now trying to look for PhD positions again, but I found out that my old prof has been speaking to other professors about me in particular. My old PI also hasn't published any of my work, and nor has he published any work since 2016. I happen to be in some city in Asia where the scientific circle is really small, so almost everyone knows one another.
Every time I get interviewed for a position, I inevitably get asked why I left my old prof. How am I supposed to explain this away?