Mobile site – images not showing correctly

My blog shows up fine on a desktop web browser, but on mobile sometimes it loads with the images in wrong places. For example my feature blog posts won’t show images or they show the wrong images (which come up a smaller).
Also have the same issue with my mobile banner – it’s sometimes showing a totally different image and is very small, so takes up only about a sixth of the banner area, with the rest of the area showing up as white space.