I have imported and renamed TIF and JPG files with the same metadata re recording date and time. Only the TIF files are imported, the JPG files remain unimproved. Thus I have in the Finder e. g. 13 image files in the same folder in which Lightroom only finds 10 files. Any ideas for resolution welcome!
Turn off the option Preferences > General > Treat JPEG Files Next To Raw Files As Separate Photos. Then do an import again. It appears that, in this instance, LR considers a TIFF to be a "raw" file.
Thank you. I think it is just the other way round: in order to get LR to consider the TIF and JPG as separate, the option has to be turned on. That seems to resolve the problem.