This bug has been around for ~15 years, ever since the .docx import filters were added to InDesign.
Adobe, please fix it already!
In addition to nonbreaking hyphens (Ctrl+Shift+_ in Word) being deleted on import, the same thing happens with optional hyphens (Ctrl+- in Word). This problem does not occur with .doc files, only with .docx.
Had this problem just recently :/
This is still around in CC 16.3
You can use RTF-Format as a work around.
Francis Brown commented
This has been around for a while, and it's easy to miss it until the production is almost done.
A workaround to this is to find all nonbreaking hyphen by searching for ^~ in Microsoft Word and replacing it by a regular hyphen prior to importing your document.
But this needs to be fixed soon. If you don't catch it soon enough in the production, you have to manually add every dropped hyphen and it can be a major time concern.
Not just importing but also copy and paste! I just got caught out with this!