I agree that this is too complicated a fact pattern to answer over the web. I recommend that you consult an employment attorney to review the contract and the discuss what took place after it was signed.
Consult a labor attorney to flesh out who the potential target could be and how, since this is a complicated situation.
If you found this "helpful" or "best answer," please click it with my appreciation. My response is for educational purposes and does not constitute legal advice nor creates an attorney client relationship which requires all the details and a personal conference.
Yes you have a colorable theory of tortious interference from your old employer as you had a signed contract in place with new employer.....all depends if you all signed a stipulation of settlement and what it says and whether with or without prejudice as to fundamental facts... I would have to review case details as to whether your seeking employment itself was a breach of contract with respects to A and therefore employer B was essentially interfering with your original contract with employer
A.....which I suspect was the basis for the now dismissed litigation.
My answer is not intended to be giving legal advice and this topic can be a complex area where the advice of a licensed attorney in your State should be obtained.