This and this - the leading slash in the template causes this to occur when RENDER_PATH_PREFIX is undefined and the context root of the application is not / (e.g. this container is deployed to a path behind a LB on a route):

I suggest adding the slash at the end of the injected env var here:
|
'/' + process.env.RENDER_PATH_PREFIX.replace(/^[\\/]+/, '').replace(/[\\/]+$/, '') : |
- a trailing slash, even if redundant should not affect route resolution, so it would be a safer default IMO.