After some testing, the reason could be…
Community Wishlist - Bitwish is a long page. When loading it on a desktop or mobile browser, if the user stays at the top, only half of that page will be loaded. The rest is loaded only after scrolling down. The point of “breakage” is exactly by the 6 vote “region”.
This gave me the idea of testing with another browser. The first report was done testing with Firefox desktop and mobile. Turns out the behavior with Chrome desktop is very similar but not exactly the same. In my tests Chrome shows 60 results (instead of the 61, also different than the 59 of Firefox). And indeed, rendering the page with Chrome desktop results in 4 out of 5 topics with 6 votes listed. Better, but still not good.
For some reason, when the page is sorted by Votes, topics seem to be lost in that jump when loading the rest of the page when users scroll down.