Query params combined with a custom url


I'm exploring using retool to build an application with a couple of pages. To make this work, I am navigating between apps passing a query param, which is used to set some defaults when each app loads.

All was working well, until I added a custom url to the main page. Now, when navigating to this app, the parameter appears briefly in the URL before vanishing, almost like a redirect. It doesn't take effect on the page.

In the editor, everything works fine as it doesn't use the custom url, but when viewing the app as a user, it breaks.

Any ideas what I might be doing wrong, or do query params and custom urls not mix?

I should add, I have tried with both normal query params and hash params.

Page settings for the main app (with a custom url):

Call to return to the app with a query param: