strange white pixels

I recently decided to take chance on Animate CC (which I'm not very used to unfortunately) in order to animate a character I created in Photoshop (latest version) who  I  eventually imported to Animate. Everything seemed okay at first, but when I tried to add a solid black background layer there were tons of white pixels (looked very blocky also) the rest of the character seemed fine, the transparency of my layers (it wasn't a flattened psd image) was on point though. I tried erasing them (with  normal eraser settings) and it didn't seem to work (the layers weren't locked or hidden). So in this situation I got back to Photoshop (where the figure was in a much larger size) and there was no sign of white pixels around the edges, I tried lowering the quality of the imported file in Animate, though the problem wasn't fixed. Would love some advice!

Thank you ❤️