Since upgrading to 2.5.4 there is a fatal error which means photos cannot be viewed
Error fetching Flickr photos: A feed could not be found at http://api.flickr.com/services/feeds/photos_public.gne?lang=en-us&format=feed-rss_200&id=131815006@N03&tags=vappu2016&per_page=20. A feed with an invalid mime type may fall victim to this error, or SimplePie was unable to auto-discover it.. Use force_feed() if you are certain this URL is a real feed.
It might be a security plugin that is blocking the fetching of the feed, or maybe we might need to force your server to use HTTPS. Or perhaps there are some characters in the photo titles or description that is causing the “SimplePie” feed reader to invalidate your photo stream. There is a ticket logged in WordPress for this problem which is in WordPress feed reader – https://core.trac.wordpress.org/ticket/21017. However there does not seem to be an obvious solution
If you add use_key=y to the slickr-flickr command it will use a different API call which uses a different library to read the photos
slickr-flickr id="131815006@N03" use_key="y" tag="vappu2016"