Refreshing Reports in Browser

I have a Power BI report that I display on a big TV in an office setting in a chrome browser. I have an plugin that automatically refreshes the page every 15 min. The first couple of refreshes will work fine and the report will load with the new dataset and everything will work as expected however after about an hour or two the Sign in button will show up on the screen and someone has to manually click it for the report to load. The pattern of when this occurs isn't apparent. I thought maybe it happend everytime the dataset was refreshed but that was wasn't the case. I also tested to see if it happened after x amount of page refreshes but that doesn't seem to be the case either. Has anyone else ran into the problem?