gif avatars are not being displayed on the profile but the small resized version shows up in the header. my gif is not too large, i've tried various sizes to test it and none of them worked.
I have the same problem too. Sometimes I must upload animated avatars up to 4 times until it showed up in both places. https://getsatisfaction.com/lastfm/topics/avatar-generator-is-not-working-again
Ok, I can reproduce this with very large gifs (over 10MB). Try right clicking on your avatar, open the image in new tab, and see if loads correctly. For the full sized image, replace 'avatar170s' with '_'. If it doesn't load properly (e.g. you see '500: Internal Server Error'), try a hard refresh, then return to your profile page (and hard refresh that too).
Perhaps the problem lies in the file size, resolution and the number of animated frames. As far as I remember, nothing like this happened on the old LFM site. I also noticed that animation spontaneously shows, sometimes LFM displays them correctly and sometimes doesn't. I tried methods that Jon gave me; fortunately, they work. But, it's a temporary fix. It seems that a weird and aggressive bug is running across LFM unchecked. It's like 500 server error; sometimes it will show and sometime it will disappear. The same goes for uploading animated avatars.