Sluggish Asset Indexing
One way to get around this is to create a new Asset Source (let’s call it “Staging”).


Add the folder of unindexed images/assets into Staging, our new asset source (which should otherwise be empty).
Now, run the asset indexer via Settings > Update Asset Indexes only for our new source, Staging.
Once the indexer has done its job, go to the Assets section of the Control Panel and drag the freshly indexed folder of images/assets from Staging to the desired Asset Source.


Repeat the above process every time you wish to index a bunch of new assets without touching the previously indexed assets.