Please be aware that texture validation warnings will generate errors, and they can no longer be ignored following the release of Fortnite Ecosystem v31.20. If the errors are not corrected, you will be unable to launch your session. Fixing these errors increases the compatibility and stability of your island across platforms.
UEFN offers a built-in way to make your texture sizes conform to UEFN requirements automatically. To do this:
In the Content Browser, select one or more invalid textures.
Right-click on a texture thumbnail and choose Conform Texture from the contextual menu.
To learn more, please visit Resizing Textures | Unreal Editor for Fortnite Documentation | Epic Developer Community