See Title
the When Clip Ends section is grayed out.
Notice that the check mark next to start playing auto is checked but I can't uncheck it because it's grayed out too.
Sounds like your video is in the pre-service loop, warmup, or post-service loop section. In these sections all videos automatically advance to the next service item, therefore the setting is disabled. Hope this clears it up.
Yep. Thanks.