My former PhD supervisor has published conclusions from my thesis without citing my thesis. Is this ok? My former PhD supervisor has just published a paper on a scientific subject investigated by me in my thesis.  The subject (or question posed), was an idea that I came up solely during my PhD and which I chose to investigate as a sub topic - my conclusions were published in my thesis in 2015 and I assume (from a legal statement in the thesis), that I own the copyright.

The paper just published has taken my hypothesis and explored it in more depth.  Some of my studies have been repeated by other people in the lab.  Moreover, some of the key conclusions made by me in my thesis have been made again.  I have not been credited in any way.

Is this plagiarism and should I pursue this?  I’ve left academia so no longer publish anyway.
My former PhD supervisor has just published a paper on a scientific subject investigated by me in my thesis...The paper [takes] my hypothesis and explored it in more depth. Some of my studies have been repeated by other people in the lab. Moreover, some of the key conclusions made by me in my thesis have been made again. I have not been credited in any way.
Is this plagiarism and should I pursue this?

This is not plagiarism: As you have noted, the paper [takes your] hypothesis and explore[s] it in more depth (emphasis added), i.e., the paper goes beyond your results to provide something new. To determine whether plagiarism appears elsewhere probably requires more information than the OP has provided.

I have not been credited in any way.

A citation to your thesis or any of your other published works would be appropriate, perhaps even required, e.g., if the paper is entirely built upon your work.