Animated gifs doubles or triples in size after optimization

[Nunardas]

Hello, I have this animated gif: http://s3cdn.observador.pt/wp-content/uploads/2017/11/21123024/capa770.gif

After the resize process it's much larger: https://imageproxy-observadorontime.netdna-ssl.com/800x,q85/http://s3cdn.observador.pt/wp-content/uploads/2017/11/21123024/capa770.gif

It seems to be a weird and not expected outcome. Is this something that could be fixed?

Thanks