Retaliation? Talk to a lawyer.

No...there would not be a pay decrease when I move to CS.
My pay has never changed (other than the $2 pay increase over the 3 year period).

Hi,
Then I doubt very much that you have good cause to quit due to a demotion. You have no raises to indicate promotions. Every job you wrote about you indicated as a temporary and not permanent position.

Although you did say some things that make me think HR is trying to get rid of you, but they want you to quit.

You've brought more than one complaint to HR they probably think you are a pain in the ....

I suggest you talk to a lawyer .. I think I see indicators of retaliation, but an attorney would have to evaluate your situation.