Step to reproduce
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1) Enable VoiceOver
2) Run the attached tests ( SpinnerDemo.java ). Actually this sample code is from https://docs.oracle.com/javase/tutorial/uiswing/examples/components/index.html#SpinnerDemo with added coded for Accessibility.
3) Once the Frame is visible. Click on the first Spinner if focus is not on it.
4) Press Up/Down arrow to change the value of the Spinner. If value are read wrong or partially then the bug is reproduced.
5) You can try the same with Mouse to change the value.

I have attached Screen Record for the same.
Note: I tried the same on windows with JAWS and it works as expected.