Images won‘t display in an entry loop

Question

Unfortunately I'm still very new to Craft, but I have a question to which I haven't found an answer here or in the Docs or the ones I found don't seem to work: Why doesn't this entry-loop output a picture? Because the image title is output correctly and the transformation medium exists.

{% for entry in craft.entries
    .section('projects')
    .limit(1) %}
<a href="{{{ entry.url }}">
    {% set image = entry.image.one() %}
    {% if image %}
        <img src="{{ image.getUrl('Medium') }}" alt="{{{ image.title }}" />
    {% endif %}
</a>
{% endfor %}

thanks for help!