For the most part setting an "event container" property (https://doc.daypilot.org/scheduler/event-containers/) on an event correctly places all items with the same container on the same line exclusively.
Under some circumstances, however, it becomes confused and will place items with different containers on the same line.
See attached screen shots with anonymized data. the label of the event is the container id (string).
In the first screenshot (7749) you can see that the last line contains events with different containers.
Moving (dragging) event "Container 2_1" to the Friday column results in screen shot 9672, where it is placed on a different line, but one also shared by a different container (0_0)
Dragging 2_1 to Tuesday, however, results in screenshot 8081, which I think is correct - each container is on a separate line.