`prev_url` not working on routed pages

There seem to be a few issues reported around prev_url not working. Related issues include:

• https://forum.grabaperch.com/forum/01-20-2016-rewrite-rule-for-pagination-not-working-for-prev-url
• https://forum.grabaperch.com/forum/05-06-2015-pagination-bug-prev-url-not-populated
• https://forum.grabaperch.com/forum/02-04-2015-pagination-previous-link-not-working

For me, prev_url stops working when I'm on a page that has been routed.

How to recreate:

1. Create a page in Runway using a master template as usual
2. Get pagination working
3. Add a route to the master page, go to a routed page, the previous url will no longer output anything

As mentioned in other threads, you can get around this using prev_page_number but it's confusing why prev_url doesn't work.

Here are some of my diagnostics:

Perch Runway: 3.0.10, PHP: 7.1.8, MySQL: mysqlnd 5.0.12-dev - 20150407 - $Id: b396954eeb2d1d9ed7902b8bae237b287f21ad9e $, with PDO
Server OS: Darwin, apache2handler
Installed apps: content (3.0.10), assets (3.0.10), categories (3.0.10), perch_blog (5.6.1), perch_forms (1.9.1)
App runtimes: <?php $apps_list = [ 'perch_blog', 'perch_forms' ];
PERCH_LOGINPATH: /perch
Image manipulation: GD Imagick
PHP limits: Max upload 32M, Max POST 32M, Memory: 128M, Total max file upload: 32M
F1: 3b606135b33e6a102526838f4152a807
Resource folder writeable: Yes
REQUEST_URI: /perch/core/settings/diagnostics/
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php