First off I love the new functional Template Editor so don’t take this the wrong way but there is a bug/annoyance which might have been overlooked.
Go to the editor and start typing e.g.
{{ states('sensor.
pause while the editor does it’s magic and updates giving:
…and then check your log. You’ll find that error is also logged there. Type slowly or use the editor a lot and you can get tons of errors.
Couldn’t errors from the template editor be supressed in the log?