Error when trying access URI with Global Function's name

I've found errors & blank pages when trying access URI with Global Function's name (testing as controller):

http://ci4.local/<controller>

Displays an error page (Service Accessors):

http://ci4.local/esc
http://ci4.local/view
http://ci4.local/helper
...

Displays a blank page (Miscellaneous Functions):

http://ci4.local/is_cli
http://ci4.local/redirect
...

PHP: 7.0.5
ENVIRONMENT: development