That’s a bug in the Automation Editor (and to many sensor domains in your code I think, as kbrown01 already said).
If you like, you can change your code that way:
{% set a = states('sensor.absolute_humidity_draussen_absolutehumidity') |float(0) %}
{% set b = states('sensor.absolute_humidity_garage_absolutehumidity') |float(0) %}
{{ (a > b) }}
will return true or false.
Avoid using states.sensor.temperature.state , instead use states('sensor.temperature') . It is strongly advised to use the states() , is_state() , state_attr() and is_state_attr() as much as possible, to avoid errors and error message when the entity isn’t ready yet (e.g., during Home Assistant startup).