Can you describe more about what you are Segmenting on? What is the expected behavior vs. what you see?
the challenge with Account field is that they will only bring in SFDC Contacts when populated. But blank fields may or may not bring up a Lead record.
If you are pointing at the Account field, I'm unsure why the Contact level would matter here unless the field was on both records and mapped. I would find it odd that a CDV wouldn't register properly.
Have you tested changing the field(s) on an Account vs. Contact to see what occurs in the logs?
I really do not understand what was told to you. If there is a change to the contact, and you segmentation is based on account fields, why would the segmentation have t change ?
We have created numerous segmentations on account fields an never observed any issue.