Greetings, gentlemen.
Problem: they migrated from Drupal to their own engine and opened up a whole series of jambs. One of them does not work out. On one of the pages was a comment module. Each comment received its own unique url and, in fact, contained a duplicate main page. Total, it turned out to accumulate the following doubles:
pagetitle%26post%3D-29647723_37
pagetitle%26post%3D-34234235_37
pagetitle%26post%3D-23425623_37
How in one fell swoop are all pages with pagetitle%26
ending in this pagetitle%26
... redirecting (301) to the only url that works today?