"Save Settings" on tokens doesn't work

So I've got a game where a player wants their character token changed, and I went in today to do that. Unfortunately, no amount of me clicking the 'Save Settings' button on the new token has saved anything (like setting up the HP bar and her darkvision). Opening up the developer panel on my browser show this error when I click the button: Any ideas why this is happening?

I am having the same issue across multiple games, everything else appears to be fine, token settings are however unable to be saved.

This is the image that doesn't appear to be where I put it:

This has been confirmed and the Devs have been notified. 

Thanks for the prompt response guys.