@AdamLowe-7183 Thanks for posting in our Q&A.
For this issue, I have done the test in my lab. Here are some screen shots I can share with you.
- I configured the local picture URL in the setting "Locked screen picture URL (Desktop only)" and deployed it to my device group.
Note: https source is not entirely necessary or required, and can be a local source too if configured like so: file:///C:/picture/lockscreenpicture.jpg
2.Wait for some time and I can see the profile shows success status in intune portal.
- I restart the device and it shows the target picture in lock screen.
Hope it will help.
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