URI malformed on dev-template

So I am trying my hand at templates, but I am having issues with testing them out. Specifically, when I go to /dev-template, I get a red “URI malformed” error where the preview should be (using the default template text).

If I remove the template text and just add a {{ states.sensor… }}, I get valid output, but if any for, if, etc. exists, it dies a horrible death. My templates in my YAML still work though. In Developer Console in Chrome, I get this:

frontend-5baa4dc….html:1 Uncaught DOMException: Failed to execute 'registerElement' on 'Document': Registration failed for type 'iron-meta'. A type with that name is already registered.
    at window.Polymer (https://[URLREMOVED]:8123/static/frontend-5baa4dc3b109ca80d4c282fb12c6c23a.html:1:1494)
    at https://[URLREMOVED]:8123/frontend/panels/dev-template-7d744ab7f7c08b6d6ad42069989de400.html:1:5708
    at https://[URLREMOVED]:8123/frontend/panels/dev-template-7d744ab7f7c08b6d6ad42069989de400.html:1:7659
window.Polymer @ frontend-5baa4dc….html:1
(anonymous) @ dev-template-7d744ab….html:1
(anonymous) @ dev-template-7d744ab….html:1
frontend-5baa4dc….html:1 Uncaught DOMException: Failed to execute 'registerElement' on 'Document': Registration failed for type 'paper-input-char-counter'. A type with that name is already registered.
    at window.Polymer (https://[URLREMOVED]:8123/static/frontend-5baa4dc3b109ca80d4c282fb12c6c23a.html:1:1494)
    at https://[URLREMOVED]:8123/frontend/panels/dev-template-7d744ab7f7c08b6d6ad42069989de400.html:1:20515

Any thoughts?

*EDIT: I should mention, I am on 0.34.5, but I was on 0.34.0 when the problem happened and updated just to see if it would fix it. It didn’t.