@Jason P, Thanks for posting in Q&A。 For the custom policy with OMA_URI with error, you can go to event viewer Applications and Services Logs > Microsoft > Windows > DeviceManagement-Enterprise-Diagnostic-Provider > Admin to see if any error with it.
For the setting which applied successfully but not working, I would like to confirm if there's any GPO set the same setting, Based as I know, if the same setting deployed via GPO, GPO will win over Intune policy.
Please check the above information and if there's any update, feel free to let us know.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.