When using Microsoft Word & PDFMaker:

Circular gradients do not have the expected gradient pattern. They have a STAR shaped gradient pattern.

This star shaped gradient pattern is more apparent as the shape that has a gradient fill becomes SMALLER.

Also, Acrobat stores these shapes and fills as a Bitmap image representation, so they are not Vector objects as expected, so they do not regenerate with scaleing.
Other PDF software, e.g. FoxIt PDF Editor, does not have this gradient pattern problem. Also it stores the shapes and gradients correctly as a Vector object.

[Note: Other unexpected patterns, may occur with other gradient styles apart from Circular]

ATTACHED are sample files that show this issue (.PDF, .DOC.)

[ Tested with WORD 2016 ]