There are a few reasons as to why this could happen:
1. Do you manage more than 100 locations?
Due to Google My Business API restrictions (What we use to connect) we are unable to pull more than 100 GMB locations. As a workaround you can split these between different Google accounts.
2. Is the location verified?
You can check this by visiting: https://business.google.com/locations - Please ensure the location in question is "Published".
3. Is your listing part of a franchise?
If you are posting to Google My Business Listing which has more than 10 locations (franchise) you will receive the following bounce message "This location belongs to a chain. The Local Post API is disabled for this location".
Unfortunately listings over 10 locations are not supported via the Google API (What we used to connect).