Append from DB playlist overlap

I have a probleme when a playlist is loaded in the playout from the DB.
The 11am playlist is ~30min time long, at 11:27 an event loads the 12am playlist, that is 1h30 time long and begins by a soft fixed time at 11:30.

It worked in that way from last september, but since a few weeks, the next hour playlist is not loaded at the bottom of the current, but overlaps last items. So the first items from 12am pl and the last items form 11am are mixed.

Here is my 11:00 generated playlist :

Here is my 12:00 generated playlist :

And here the result once the 11:27 event loaded the pl :

You can see that 2 items from the 12:00 playlist are loaded before the End of hour dummy item.

I use the “Append playlist from database” event.
I have 3 types of events to load a playlist :
“Load…” + “Load and play”, “Insert…” + “Insert and play” and “Append…” (I translate back in english from french, so I don’t know if are the correct names)

So what is the difference between that 3 types, and which of theml can I use to be sure that the next hour playlist be loaded at the very end of the current playlist items ?