I seem to be experiencing this and see a history of similar problems - but nothing recently.
Verion 2015r2.4, windows debug and linux build.
New clue: when set to multiline mode, the content appears on the labels. When not in multiline mode, content does not appear.
Other info: when setting a style, the background color of the style does appear for the label, but the content (text) does not appear - regardless of which colors I choose (so far).
Thanks for the info.
I also experienced that.
Use a WebCanvas instead.
Certainly looks like it. I added that problem occurs for label on dialog, not necessarily has to be in a container.
Is there a way to have the font statement for DrawString reference a font family, to accomplish what a style assignment provides?
Yes, but fonts may not be installed on the server, so that will be a problem especially on most Linux hosts.
The other workaround is to use a Read only TextField styled with a transparent background and borders width 0. It will use client side fonts, so you can use any typeface family.
WebCanvas relies on fonts being on the user’s computer, not the server.
Great 
I must have confused with DrawString to a picture Graphics object. Thank you.