Invalidate cache from two channel expiry dates
the error was with the date format in the date comparison conditional and the until tag instead of unless

{% if currentTime &lt;= newsDate | date('c') %} {# those two dates were formated differentely #}
    {% set invalidate = newsDate.expiryDate | date('c') %}
{% else %}
    {% set invalidate = auffuehrung.konzertStartdate |date('c') %}
{% endif %}

{% cache until invalidate %} {# not unless #}
 {# blablabla #}
{% endcache %}