There are two main reasons ‘Unknown’ individuals may appear in your tree online after you sync it from Family Tree Builder:
1) Privatized individual in Family Tree Builder
Open your project in Family Tree Builder.
Search the name of the person that appears as ‘unknown’ on your family site.
On the person’s card, click on the ‘Edit’ button and then move the mouse to ‘Edit Details: <NAME>‘
On the new window that appears, click on the ‘More’ tab.
At the bottom of the screen there is a check box ‘This person is private (do not sync to family site)’.
Uncheck the box and sync your family tree to your family site.
2) Display and Data language in Family Tree Builder
In Family Tree Builder, it is possible to choose a DISPLAY language and a DATA language.
DISPLAY language corresponds to all the buttons and command names in the program. It only changes Family Tree Builder’s interface and will not affect any information that you have manually entered in the tree.
You can open the ‘Languages’ window by going to ‘Tools’ menu in the upper toolbar and selecting ‘Languages’.
On the new window that opens you can see the current settings of the DISPLAY, the Primary and the Secondary Data languages.
Problems may arise if you change the DISPLAY language along with Primary Data language. This will create the new language for your project, and even if you add data using the same language characters as before, you will do so under a new data language. Thus some information in your project will be added under one language, and some under another language.
You started your project in Family Tree Builder in Spanish and added some amount of data. Then you switched the display language to English, and this changed the main data language as well.
Thus the new language for your project was added. You continued adding information in Spanish, but in fact it was added under English language. That’s why when you switch your language back to Spanish, you see ‘Unknown’ instead of data you entered recently.
To have it fixed without adding data manually please read the following article: How do I copy data from one language to another?