Annotations for 3 HTML pages with distinct URLs are *aggregated* at Hypothes.is/search (but on the 3 lesswrong.com webpages, annotations are shown correctly)

### probably a very similar problem to

https://github.com/hypothesis/support/issues/84

### other issues that could be related

https://github.com/hypothesis/product-backlog/issues/493

https://github.com/hypothesis/h/issues/6216

https://github.com/hypothesis/h/issues/2921

### Steps to reproduce

https://hypothes.is/users/martin_m_n_novy?q=tag%3Ahypothesis-h-issues-6702

### Expected behaviour
3 distinct titles and URLs should be shown

### Actual behaviour
1 title and 1 URL is shown, and all the annotations for the 3 distinct webpages are aggregated **as if** the 3 webpages had the same title (they have distinct titles on the web)

### Browser/system information
Edge and Chrome, updated, Windows 10

### Additional details

the URL

https://api.hypothes.is/api/search?tag=hypothesis-h-issues-6702&user=acct:martin_m_n_novy@hypothes.is

helped me in diagnosis.

The output is at https://gist.github.com/martin12333/6099734d7a425424b1292c37b97ae34b , with 2 strange lines marked by ///////

### (Could the problem be related to an incorrect equivalence of HTML documents? No, the 3 webpages are not considered equivalent.)
(https://github.com/hypothesis/h/issues/6576)