To reproduce:

1. Go to homepage
2. Click an image post so it expands to full size within the feed
3. Wait a few moments for someone to post something which triggers a feed refresh (or something)
4. Notice that the image that you were just trying to view has been “unexpanded” so you have to click it again.

I notice that this is not a problem on lemmy.ml so maybe this is fixed in 0.18.x