Missing files or Empty DCIM folder on Android

I was recently backing up my android phone to transfer files over to a new phone when I noticed that the DCIM folder was only showing the latest 100 or so photos when connected to my laptop, when I knew I must have had at least 1000 on the device. Oddly enough they also weren't showing up while using a file manager either.

Clearing the cache and data for External Storage and Media Storage allowed all of the files to show up again for me.

Solution

1. Go to Settings -> Apps

2. On the top right tap on the ⋮ (tree vertical dots) and select Show system

3. Select External Storage, tap on Storage and tap on Clear cache and Clear data

4. Go back, and find Media Storage, tap on Storage and tap on Clear cache and Clear data

5. Restart your phone

Source

Google Product Forums Solution