A PNG file imported in Photoshop CC 2018 does not show up correctly but is displayed as a mosaic with bits of other files in it.
- Go to Preferences > Plug-Ins > Filters & Extension Panels and select the boxes in the screenshot below.
- Restart Photoshop and open your PNG again.
This disables CC libraries but PNG is displayed correctly.
As a workaround convert PNG to JPG or PSD.