Hi Joni thanks for your post! To clarify are you using org chart shapes to do this or another type of shape? If you'd be willing to share a screenshot of one of your shapes where text is disappearing that would be helpful.

I am creating my own diagram key and am using a rectangle shape.    

Hi Joni thanks! There are two types of text behaviors in Lucidchart which I've demonstrated with a rectangle shape in the GIFs below.

First if you have your font set to a specific size your shape will automatically expand in size in order to accommodate your font at that set size. 

Alternatively if you set your font size to "auto" your shape will remain at the same same and your text will automatically resize to fit within the boundaries of the shape. 

Are you experiencing something different than this? If so a screenshot would be very helpful so I can better understand what's happening. Thanks for your help and patience!