The fact that the speed of the converted gif doesn't always match that of the initial gif isn't a bug and is normal. From what I observed, the converter on xat only takes into account the number of frames (number of "images") that there are in a gif without taking into account the time with which the frames are running. So if in a gif there are few frames but the transition between them is long, the gif will look fast on xat. The solution to this would be to be able to use the initial gif directly without converting it. For now, you can either choose a gif with enough frames, or you can use an image editing software to repeat some frames.