Apple Photos Crash/Loss of Photos

Some additional information we need:

• how much free space on your boot drive?
• how big is your library, i.e. how many photos?
• where is your library located? If on an external HD how is that HD formatted and connected to your Mac?
• did you apply any updates or upgrades just prior to the problem occurring?
• are you running a "managed" or "referenced" library?

have you run any "cleaning" or "optimizing" apps on your Mac?

You can only restore an entire library, not specific albums from Time Machine. If you have room restore the library to another location, Desktop, external HD, etc., by Control (right) - clicking on the library and select this contextual menu option:

When restored you can open it and export just those albums to folders on the Desktop. Then open your current library and import those folders from the Desktop.

The simple answer is to restore your TM backup - but we really need more information to be positive - what exactly is missing? What are your iCLoud settings on the Mac (is iCLoud Photo Library enabled and if so is optimize photos on this Mac checked or download originals to this Mac?

Instructions for TimeMachine are here - Use Time Machine to back up or restore your Mac - Apple Support - and FAQs and trouble shooting hints here - http://pondini.org/TM/FAQ.html

LN

The triangles appear, if Photos cannot find the original image files.

Have you been running any cleaning applications to remove duplicates, before the crash appeared, for example CleanMyMac? This can be causing such crashes and missing photos.

Sometimes the photos are still in the library. Select one of the thumbnails with the triangles, then enter the key combination ⌘I to open the Info panel. Copy the filename from the Info panel and search for this file using Spotlight or Find Any File.

When I search my library, Spotlight will usually find the files inside the package. But if Spotlight does not find it, download FindAnyFile - the free trial version will suffice to search you Mac for the filename.

You can download and try it here: http://apps.tempel.org/FindAnyFile/index.php

if you can find the missing photos, copy them to a folder outside the library.

Then I would try to repair the library (see here: https://help.apple.com/photos/mac/1.2/?lang=en#/pht6be18f93)

and reimport the missing photos.

Make a backup copy of the library, but do not overwrite any existing olde backup copy.

Are the missing photos gone completely from the Photos Library, or just missing from the three albums?

Have you checked in Photos view in photos, if you scroll to the dates where the photos should appear in the moments, collections, years?

Are you syncing your Photos Library with iCloud? Then restoring the library from Time Machine will result in a new upload to iCloud.

it appears that the triangular thumbnail AND the photo to the immediate left of it are both the same.

It is good to know, that your photos are still there.

Compare the pixel size of the photos. Do the versions with the warning exclamation point have the same width and height as the photos to the left?

Or are the problematic photos perhaps RAW versions?