Yesterday, my wife imported 350 images from her camera's SD card from her sister's wedding (thus, quite important images), and as we have BackBlaze installed on her macbook for cloud backup, we have been able to confirm via. the backblaze interface that at least about 50 of them have been backed up to backblaze, which means that they must have been on the computer as backblaze does not back up files from external sources.
We have tried with local Time Machine (but the disk only has 20GB left, so Time Machine didn't have much), Disk Drill to see if they were deleted, but haven't found them yet (Disk Drill is still running), and they are not in the trash neither. Neither of us have had the terminal opened, so it shouldn't be a rouge terminal command either.
Disk Drill on the SD card is not an option, as they have since been overwritten sadly.
We have more or less given up on getting the images back, but we still can't figure out how the files could disappear with no trace like this. If anyone has any ideas about what we could do, please let us know.