Not sure if you solved your route issue. But I ran into the same issue with my routes, and seemed like I needed to add - ‘#modelascontrollerroutes’ to the “After” block of myroutes, like this;
Name: approutes
After:
- '#rootroutes'
- '#coreroutes'
- '#modelascontrollerroutes'
---
The reason is that #modelascontrollerroutes (/vendor/silverstripe/cms/_config/routes.yml) have the following line;
'': 'SilverStripe\CMS\Controllers\RootURLController'