There are several forum discussions about "404 Not Found" for ORDS upgrades for various versions.
For that reason baby-steps to fix this for the most recent ORDS 17.4.1 are needed especially for APEX setups.
It wouldn't hurt to still have glassfish-version of steps, even when its support will be discontinued.
I start with the situation
1.) https://host:port/apex

2.) https://host:port/i/apex_version.txt
Application Express Version: 5.1.4
And then what?
rgrds vaaPo