It seems that custom pages aren't routing properly when the base_url setting is used.

To reproduce, with Datasette 0.55.

Create a templates/pages/custom.html with some text.

mkdir -p templates/pages/
echo "Hello, world!" > templates/pages/custom.html

Start Datasette.

datasette --template-dir templates/

Visit http://localhost:8001/custom and see "Hello, world!".

Start Datasette with a base_url.

datasette --template-dir templates/ --setting base_url /prefix/

Visit http://localhost:8001/prefix/custom and see a "Database not found: custom" 404.

Note that like all routes, http://localhost:8001/custom still works when run with base_url.