Photos

The ! means that the app cannot find the original file.

Are you running a Managed or a Referenced Library?

A Managed Library, is the default setting, and Photos copies files into the Photos Library when Importing. The files are then stored within the Library package

A Referenced Library is when Photos is NOT copying the files into the Photos Library when importing because you made a change at Photo -> Preferences -> General. (You unchecked the option to copy files into the Library on import) The files are then stored where ever you put them and not in the Library package. In this scenario you are responsible for the File Management.

Have you been using any apps that "clean" or "tune up" your Mac recently?

Do you have a back up?

Whitehairednancy wrote:

My pictures are not downloading properly. I continuously get the triangle with an! ...

Where are you downloading from? From a camera or card? From an iPhone? From iCloud?

The format of the image files may be incompatible, so Photos cannot process the image files.

Are you shooting RAW? If yes, what is the model of your camera and which system version is running on your Mac?