Trouble updating Schedule helper

Once I create a schedule it seems I can no longer update if I try to change it to a half-hour block. Changing it by a full hour, on the hour, will work, and the update sticks. But if I try to extend or shorten a block by a half hour, the change isn’t recorded. Is this a KI?

Similar issue here, the issue for me is that I can’t update anything on Sunday

This happens also on an empty schedule