Animated gif images do not animate properly

Hello,

I'm trying to use an animated gif images in my project and some gifs works properly; some it does not animate at all and displayed as the still image; the others does animate but the loop delay is much longer than expected. Can you please check and advise what should I check/do to improve that? All the GIF images are provided from my customers so I cannot decide the tool to create them but I can modify them (programmatically) before using it, all the gif images work properly in web or viewer.

Thank you and I look forward to hearing feedback from you