Pictures disappearing in HTML 5

I have a problem where some images in my published content disappear after I leave a page and then re-visit it.

I am working on my desktop and uploading the published content onto a web server. I have tried looking at the files on Chrome and Safari and mobile safari on the iPad. All show the same problem.

The pictures are a mix of pngs and jpgs. Some of them are on a master page, some are on the screen and some are on buttons. (Yes there are a lot of pictures.) After the pictures disappear, the ones on the button states will reappear if I move my cursor over them (or gently swipe a finger across them on the iPad).

At the same time as the pictures disappear, the navigation locks up and none of the buttons, including the player buttons (prev, next etc) will work. By hovering the mouse over each button until all the button images are restored, I can unlock the navigation until the next time I return to the page. However, the static images on the page never return, and random images throughout the program are missing from that point onwards.

I shared the story file with a colleague in another office who said he had the same problem until he re-published using version 1.5 (specifically 1.5.1401.2415) I am running Articulate version 1.6 (specifically 1.6.1407.2208). My colleagues in the same office, running the same version as me encounter the same problem. 

Please can you suggest why this might be happening and perhaps suggest a solution? 

Is it possible to downgrade my version of articulate to version 1.5?

Due to client confidentiality, I cannot share my story files.