I have a setup in klwp that displays a random image from a folder of about 15 pictures and changes every hour. After a week or so I noticed there were a few pictures that still hadn't come up. I opened up the folder in a file browser to make sure the images were still there, and noticed all and only the ones that hadn't showed up all ended with .jpeg. I changed all the .jpeg names to .jpg, restarted klwp, and the first image to be randomly picked is one of the ones that wasn't before.
Did a bit of testing. I added an image to klwp with a formula file:///image.jpeg. Worked fine. When I changed the formula to the random image utility set to a folder with only .jpegs, the image was blank. So it seems to be a problem with the timer utility.
Using klwp 3.32b819808 (current on play store as of 7/23/18) on a Moto g5 plus with Android 7.0