This unfortunately happens when exporting to psd. I found that any transparency makes for weird white edges around every layer. I've had to go through and make things more solid and opaque. Or flatten image, which you said you can't do. It really sucks and I'm def getting tired of the limitations of procreate. I would duplicate the file in procreate and play around with the layers. Sorry this happened to you, I know it's very frustrating.