So in the first iteration of this post I seem to have found why the widget doesn't work: Valve recently made Steam Store links more readable by putting the name of the game behing the AppID which turns
In the preview at least the text works, made posting Free Game Threads just a little bit more annoying than it needed to be.
The code/RegEx seems outdated in the way that the old URLs still work, the added game name screws it up though.
With game name:
Old URL syntax:
TL;DR: Until the code is updated, remove game name from URL to make Steam Widget work.