if you change your major then you should have OPT again bah.
You cna ask some lawyer , I know on fanlaw.com you can ask them any questions and you can ask another 1-2 lawyers, sometimes they say diffrent tthings.
If they said the same, you can be sure.

I know the law just changed , so like for same major, after BS,MS,and PHD you should have 1 years of OPT after you got each degree.
So I assume once your major changed, you should also got the OPT.
Since now you should be trained for another career.
But whatever people said here is non professional , you can ask some lawyer, just call them and ask.