Recently thumbnailing of GIFs was re-enabled on Wikimedia sites after new code was added to count the frames in animated GIFs.
Reading the code it appears that currently two checks are intended to determine whether a GIF should be thumbnailed.
First, if height*width*frames > $wgMaxImageArea then Bitmap.php aborts and no thumbnail is attempted.
Secondly, if height*width > $wgMaxAnimatedGifArea then Bitmap.php returns only the first frame.
The default values for these parameters are 12.5 million and 1 million respectively, and they do not appear to have been changed in Wikimedia's CommonSettings.php file.
Now there appear to be two issues here. First, since we are now counting GIF frames, is there a reason for still having the second check? My understanding is that the lower limit was added in the days before frame counting to trap large animated GIFs with many frame before they could crash the thumbnailer. Now that we count frames, isn't the first check sufficient for that?
Secondly, and the more immediate reason for this bug report, it appears that Wikimedia is showing single frames for some animated GIFs even if their size is definitely less than one megapixel. For example:
Each of these is an animated GIF with an area less than 1 megapixel but the thumbnails shown on the image description page (and anywhere else thumbnails appear) show only a still image. Hence they appear to have triggered the second conditional even though they shouldn't have if the sizes are being accurately handled and the limit is still set at the default.