Hi Eswaran,
We have set the MaximumDropDownHeight to 50 and the control as at the bottom of the screen to all the availble space is above the control,
I have uploaded a video and project demonstrating this issue,
We have replicated this issue on a number of devices
https://www.dropbox.com/s/znbtu6larmyctcx/ComboBox.zip?dl=0
Regards,
Shane