I play the pocket edition and i have issue with mind blocks are invisible and can't be minded

I was playing and testing near my hout i want to expand the area of block so I minded some blocks but when I started to minded the block it was invisible and can't pick up in my inventory and when I re started the app the minded block is visible to the spot that I minded 

This is my seed -7167435447839276314

My cordinate (-439,120,390)