Photos that I captured could be able to view in Camera roll for few minutes. But after that those images could not view and converted to grey thumbnail. After I came back I connected phone to PC and copied those images and there were three files with different extensions as below image. I could not able to view the .jpg image still. Please help to recover lost images. Now SD card work well as previous and save images to camera roll as well.
The two files below the
.jpg image in the screenshot are created by the Lumia Camera whenever you capture an image with HDR mode and/or Rich Capture switched on.
Those files are essentially backups of the image and they allow you to readjust the brightness of, or choose to save a different frame of a "rich image".
Try opening the jpg image on your computer, because everything seems to be in order. It might be a problem with the Photos app. Also, try navigating to the photo files using the Files app or the Windows 10 Mobile File Manager and try opening the image from there.