Saw a new little paragraph on this beauty here for ifchanged. However,
{% ifchanged %}
(<i>Updated</i> {{ content.updated|datetimeformat('%Y/%m/%d') }})
{% endifchanged %}
these three lines load a white screen on ALL blog posts. Blog listings, I believe, were unaffected.
//edit: goal is, if content was updated after publishing, then include “(Updated [date])” text.