Now, SomeHelperClass and OtherHelperClass sit in the global namespace so in the code :
\OtherHelperClass::some_simple_method();
Accessing clasess from other dirs works as well:
\SomeNamespace\ClassA::some_method();
After migtation to PHP7.1 it doesn't work.
The quick workaround is to add all the classes to the autoloader in application's bootstrap file, but it may be a bit of pain with large number of classes.
SomeHelperClass.php is an illegal filename, Fuel requires all files to be lowercase. See https://docs.fuelphp.com/general/coding_standards.html under "File Naming".
You could get away with a filename like this on Windows (because the filesystem is case insensitive), but not in Linux (and MacOS depending on the configuration).