I experienced this in the past and to the current version that images from the previous pages disappear from the left preview and on the slide itself. I though it was my convention of name file saving of .png images having long names or spaces as I try to shorten it with no spaces will prevent it from recurring. It also happens with .jpg.
That is a serious bug/problem. When you are able to replicate the problem, please provide a sample file (with problematic images) and describe it at https://www.libreoffice.org/get-help/bug/
There have been problems with images disappearing from presentations, since v3.3 (refer bug fdo#46477). Appears to have possibly been fixed in v4.3, although as that bug indicates, the situation is not entirely clear.