Dunno if this only applies to me, but, as of now, e621 is correctly displaying post previews as well as actually allowing me to click on them and not being forced to use the "Random Post" button.
Is it possible the website was updated to work on legacy browsers? This e-reader already updated a while ago and it's apparently based on something like Android 3 (at least that's what some websites detect, may just be from this browser, even though the very limited OS this is running is based on Linux [like everything else these days].)
Have any changes taken effect lately? This is great news. I hope this means other old devices will run e621 with similar results.