Example of the not working links:
https://www.example.com/viewtopic.php?t=9432
https://www.example.com/viewtopic.php?t=9444
But these work:
https://www.example.com/viewtopic.php?t=9432&start=30
https://www.example.com/viewtopic.php?t=9444&start=8
Only some of the links do this, while others still work.