background on tablet erratic

On my android tablet the backgroun image instead of owerflow on the screen tends to stretch.only rotating the tablet to horizontasl then vertical again it fits almost well. Why? And lot of times i saw the same background image cut at different measures under the bsckground itself dfuring loading, as if there is a “backgound under the background”,at different sizes than the background one. Don’t know if i’m uncleasr, unfortunately i cant make screenshots of that secon issue because it last few seconds..
Erratic image https://postimg.org/image/iw8q7kje7/

Correct image after tablet rotate
https://postimg.org/image/wbxunxxj7/