@Aran Billen,Thanks for posting in Q&A.
From your description, I know you have configured correct wallpaper's size and URLs but got some error.
For the custom wallpaper does not appear correctly, you can try to delete it and re-create it to see if the issue can be fixed.
For Kiosk mode custom lock screen wallpaper, you can enable screen saver and configure it to see if this setting can meet your requirement.
For enabling camera app in Kiosk mode, here is a link you can refer.
https://www.reddit.com/r/Intune/comments/vcs3yt/android_enterprise_kiosk_mode_camera/
Non-official, just for reference.
If above information cannot solve your issue, it is recommended that you open an online case to get more help.
Thanks for your kind understanding.
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