Hi,
I have created this demo, where you can see its not working as it should.
docs.dhtmlx.com/gantt/snippet/d2ec563a
If you try and drag Task #2 down to Project #2 you can’t.
But if you remove Task #3 from the code, you can now drag Task #2 down to Project #2 - But after that, you can’t drag Task #1 down to Project #2 - because it has a hidden Task on it.
Hope it make sense.