collapse behavior not working in Ipad horizontal

I have 6 square content within 3 column, it’s ok with desktop and mobile, i just have problem with ipad horizontal version, the last 2 square are not put together left and right , they’re stack in a upper and bottom manner;

just like this.
V

************** **************
* * * *
* * * *
* * * *
* * * *
* * * *
************** **************

************** **************
* * * *
* * * *
* * * *
* * * *
* * * *
************** **************
**************
* *
* *
* *
* *
* *
**************
**************
* *
* *
* *
* *
* *
**************