The issue of a "trail" being left in GIF exports from Spine could be related to several factors. One common cause is the handling of transparency and color limitations inherent in the GIF format, which supports only 256 colors and a single transparency color. This can lead to artifacts or trails if the color palette is not optimized for the animation. Additionally, if the export settings in Spine are not configured correctly, such as not using the "Premultiply Alpha" option, it can result in unwanted artifacts. The choice of 8/16 bit color in Photoshop should not directly affect the GIF export from Spine, as GIFs are limited to 8-bit color. However, ensuring that the color palette is well-suited for the animation can help reduce such issues.

To address this, you might want to experiment with different export settings in Spine, such as adjusting the quality or using the "Premultiply Alpha" option. Additionally, reviewing the color palette used in the GIF export to ensure it is optimized for the animation can help minimize trails and other artifacts.

Try setting Speed to 1. Export will be slower, but higher quality.

Since it appears your GIF doesn't need transparency, uncheck Transparent.

Great! We'll change the default to speed=1, as it's easy to miss that speed (of the GIF processing, not resulting GIF animation) affects quality.