Issue Description
You have created a dimension string that includes windows and doors, but the height value for these elements are missing.
Solution
Here are some common scenarios that could cause the issue:
A. Caused by a slightly slated wall, that contains the window / door.
B. In Dimension Default Setting > Dimension Type, the checkmark for Static Dimension is active.
C. In Dimension Default Setting > Dimension Details, the checkmark by Display the Height of Openings as well is missing.