Check and remove repeat entries from loop
I'd probably try to filter those out in your initial query, but if you've already got them, something like this should work:

{% set existingIds = [] %}

{% for event in events %}
    {% if event.id not in existingIds %}
        {{ event.title }}

        {% set existingIds = existingIds|merge([event.id]) %}
    {% endif %}
{% endfor %}