Cannot import older photos on Photos

Are you importing the photos from an external volume? Photos 5 may have problems with the access rights on an external volume, for example, if the volume has been used for Time Machine formats or the file system format is not MacOS Extended (Journaled). Are the filename plain image numbers, or do the filenames contain long texts with ethnic characters?

If you are importing from an external volume, and the volume is rather old, I would check the drive with Disk Utility, if the volume has any hardware problems. JPEGs can become corrupted over time, if a volume is developing bad blocks.

Then test, if you can import the files, if you copy them to a local folder on your Mac.

Can the Preview.app open the problematic files?

Are the permissions in different folders OK?

A few weeks ago I noticed that just one folder behaving OK an external photos archive disk, when copied to another disk, refused to open (weird). For some strange reason it had incorrect permissions (AFAIR the staff group was missing etc. I could have added staff by Option-clicking the + but ended using the parent folder's "make all permissions inside the same" command which added the staff and reset other permissions as defaults).

Previously I have noticed that some folders copied from the network or via sneakernet from Windows have had some permissions flaws. Usually those go unnoticed, though.

If you cannot even import JPEGs, you may simply be importing too many photos at once. Photos 5 on Catalina cannot import two image files with the same file name in one import session. For example, if you are importing two folders A and B at the same time and there is a file IMG_0001 both in folder A and B, Photos will simply stop the import, once it encounters the second IMG_0001. The safest way to avoid this problem is to import only one folder at a time.

What is the format of the photos you cannot import?

After the transition to 64-bit application on macOS Catalina, the system does no longer support all formats for phots and videos. If you encounter photos or videos, that cannot be imported on your Catalina Mac, convert them to a supported format.

I am using this list for (written for iMovie) as a guide, which image formats are now safe to use on a Catalina Mac: About incompatible media in iMovie for macOS - Apple Support

Do the conversion on your Mojave Mac. The Catalina Mac may no longer have any software at all to convert some of the older formats.

Try to stick with these formats for photos - they are compatible with iMovie at least:

• BMP
• GIF
• HEIF
• JPEG
• PNG
• PSD
• RAW
• TGA
• TIFF

But as I am having frequently problems with BMP and TGA files and HEIF created by third-party apps, I am avoiding them too and are only keeping HEIC files created by my iPhone or the Preview.app.

Are the offending photos any different? FWIW, just yesterday I noticed that Catalina photos didn't import any of the five photos when one of them happened to have a name like 2020-0101-1200-00.jpg_original (it was there unintentionally because Finder didn't yet update it to be visible while I was testing photos where the date was displayed as 0.00.00*. But I digress...). Omitting that image from the folder fixed the problem.

* That time error plagued also Google Photos and could be fixed by mangling the metadata which WAS OK but those apps didn't grab the correct time. Obviously the ORDER in which the metadata was in the .jpg confused Photos.app and Google Photos. Weird. I had hunderds such .jpg that Photos 4.0 and 5.0 sorted at midnight at random order although the EXIF date was correct. I can filter those about 500 offending images out from the rest 30 000 images with exiftool and then fix and re-import them to Photos. More details for the terminally interested at:

https://exiftool.org/forum/index.php?topic=11581.0