Sometimes doesn't display at all

Regarding “sometimes it shows up,” remember that the data is retrieved from Google, bringing yet another server into the equation. When your timeline does not appear, the data may simply not be getting delivered correctly from Google. Unfortunately, it’s hard to troubleshoot more specifically without a reproducible test case.

Regarding the 404 for the CSS file, I’m guessing that you removed the font configuration from your shortcode. This looks like a bug, where our software doesn’t correctly respond to the absence of any font. We’ll mark that for fixing, but in the meantime, the easiest way to avoid the 404 error is to choose a font from the options provided in the authoring tool. If you don’t like any of them, you’ll have to tolerate the 404 for a short while until the plugin is updated.