How do I apply standard shader with emission to sprites?

Hello,

For post-processing bloom in a 2D project I have created a certain material with emission, the material uses the standard shader (where you can toggle on emission in the inspector). I have a filled circle shaped sprite (don't know where I got it from), I can apply that material to this sprite and the bloom works perfectly: a glowing circle.

For the other sprites I have I can't use the standard shader. The sprites either turn into filled squares or the rough shape of the sprite gets filled completely by one color. I am getting the sprites from a colleague, we've tried using GIMP and other programs and the images seem to be clean from any glows or artefacts. Yet we cannot manage to get a shape clearly displayed with the standard shader. What are we doing wrong? To be clear the sprites display normally with default sprite shader, but there's no emission setting in a mat using sprite shader.

I have copied the same import settings to the sprites as the circle. Sadly to no avail.