I think there was a change to routing priorities in 8.5.
In this URL, “bc_proclamaton” is a view contextual filter:
https://www.courthouselibrary.ca/search/bc_proclamation?query=Judge
In this URL, “catalogue” is a route defined in my module. But it sits in the same place as "bc_proclamation"
https://www.courthouselibrary.ca/search/catalogue?query=Judge
This worked properly in 8.4, but in 8.5 "catalogue" is being treated as a contextual filter too.
This was confirmed by deleting the contextual filter from the view, which fixed the custom module.