Pictures missing from Internal Storage\DCIM\1xxApple folders

Hi Steve and others who have this problem and find this post. I had the same issue and none of the suggested solutions helped me at all. I try to back up to a PC running Windows 10. What I did find it that if you start the process of emailing the photos from the iPhone (I was going to send a bunch of emails to myself with a few photos each in order to back them up on my PC) through the part where the iPhone is done "Processing", the Internal Storage as seen on File Explorer will start to include the photos selected for the email. You can then cancel sending the email, and use File Explorer to move them in bulk. I've successfully tried this with up to 100 photos.

I don't know why your pictures don't show up in Explorer. You could try deleting the driver. With the phone connected to the computer go to Device Manager, delete the driver below, disconnect the phone, reboot the computer and reconnect the phone. The driver will reinstall.

Regarding the number of DCIM folders, iOS creates new ones (every month I believe) but if you delete all the pictures, all the DCIMs are deleted as well and the process restarts.

Try importing the pictures instead of copying them. See this article for details.

Import photos and videos from your iPhone, iPad, or iPod touch - Apple Support

I am having the exact same issue as Steve (iPhone 6S+). I've been doing this for years as I take company pictures and download them in Windows Explorer after each trip. Recently I went to copy the pictures over since you can know longer cut (this was changed a few years back on some iOS update) and found there are large gaps in the dates. The pictures still show up in the complete photo album but don't show up in Windows Explorer (WIN7). I noticed recently iTunes pops up where for about a year and 1/2 I had to accept permission to access the iPhone drive when I plugged in the USB/Lightning cable. I close out iTunes but the drive is already accessible. Could this be a cloud backup thing? And why did it suddenly start? I sure liked the ease of doing it in explorer.