Happens a lot since 5.5. This is non VT textures by the way. I had textures load in editor very slowly on meshes, several seconds, refuse to load full resolution and sit on lowest mip. I had also textures turn black in content editor like mentioned here but also white. While clicking black textures in content browser causes their sudden load, the white ones reacted to the “preview platform” button that is in texture view. Is this one new? I switched to windows from editor platform and white texture loaded. It was checkerboard in the texture viewer before.
TLDR: Entire texturing in 5.5 is completely bugged.