Or the read thread is not ready providing full information. e.g. textures will be decompressed in order of MIP (LOD level). The smaller levels - very coarse textures - you downloaded and decompressed already, they are seen on a distance. The detailed ones you want to see when you fly over are not filled in yet (not downloaded, or not decompressed completely), which is indicated with a null pointer. Proper handling in this case is to show the coarse textures again.. keep the existing resource.. and wait for the next x frames. This causes photogrammetry popping. Detail is delayed for some reason. When no texture LOD level available at all, you get the null pointer situation. I think addins can cause this, if there is an error in the textures. Server issues could cause it too, but that would be handled differently. Default (off-line) textures are used instead.
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