Some thumbnails appear corrupt after DNG conversion

HI - I'm uploading raw Sony files to Camera Raw. I then export from there as Lossless compressed DNG files. When I view some of the thumbnails of the converted images in finder, they appear corrupted, very dark with a huge green cast. However, not all of the thumbnails appear this way, some look normal. When I open the 'corrupted' files in LR classic they look perfect. Does anyone know why some random files, that have been converted to DNG, should appear this way and can I do anything to stop it? Thanks