That's just the game loading. It can take a while to fully load in sometimes.
If this happens before you've reached the nexus, that's just because the game hasn't fully loaded yet. If it's after that, it's probably a mistake. Please fill out a feedback form reporting it, thanks!
Check if an exclamation point in a circle icon appears in the bottom left of the slideshow menu. If it does, click it, and enable autoplay. If no option to enable autoplay appears, refreshing the page may help, but is not guaranteed to.Â
This is usually the result of switching between slides too fast. Clicking on the diary and then exiting out of it will usually fix the problem, but if it persists, you may want to reload the page.
This is usually because the game is still loading in, or a result of clicking too fast, especially for slides with gifs. Reloading the page and clicking slower may help, but if this happens to you, please fill out a feedback form reporting which slide numbers were affected. Thanks!
As a general note, the Google Slides version tends to be more prone to issues than the Powerpoint version. If you continuously run into issues in browser, I would recommend trying the downloadable file instead if possible.