There seems to be a bit of confusion in this thread concerning CI= at the start of the Build command.
This is to be expected if your build is throwing warnings.
By default CI is set to true.
When it is true warnings are treated as errors, and errors cause your build to fail.
Having CI= sets the CI environment variable to false, and allows your build to complete successfully even when it is throwing warnings that you don’t intend to fix.
It is mentioned as a reserved environment variable here:
https://docs.netlify.com/configure-builds/environment-variables/#netlify-configuration-variables
The behavior is explained in more detail here:
https://docs.netlify.com/configure-builds/troubleshooting-tips/#build-fails-on-warning-message
This doesn’t seem correct.
It remains necessary as long as the build is throwing warnings that the developer wants to ignore.
Regarding the “Page not found” issue, what do you have for your Build configuration?
https://docs.netlify.com/configure-builds/overview/#build-settings