I had twitter cards working via the twitter plug-in. It has stopped working although I have changed no aspect of the plug-ins or updates.
Here is an example page where it was working (images now gone):
Here is an example where it stopped working:
The card for your website will look a little something like this!
Unable to render Card preview
INFO: Page fetched successfully
WARN: No metatags found
I have removed all plugins to test and it still produces the same errors.