Oracle - Can't login with "/ as sysdba", but can with "sys as sysdba"

I've been working on setting up a docker container running Oracle DB XE 18.4.0. I have the container built from Oracle's dockerfiles and it is working fine, except that I cannot login using

connect / as sysdba

in a sqlplus prompt from inside the container, but

connect sys as sysdba

does work. The error message that I receive is

ORA-01017: invalid username/password; logon denied

I checked that my $ORACLE_HOME and $ORACLE_SID environment variables were set and they look fine. I'm trying to install APEX in this container and the first error that is displayed when running the install script is the failed login error above where the script runs connect / as sysdba.

When installing Apex on the local instance of Oracle DB on my development environment, Everything works as expected.

I am working from a Windows 10 (1803) machine which is running docker 18.03.0-ce with a VirtualBox 6.0.2 setup.

Thanks to @BalazsPapp who pointed this out in the comment to my question.

To use conn / as sysdba, I had to be logged in as the user oracle instead of root.

Switching to the oracle user and attempting to login again solved the problem.

StackExchange Database Administrators Q#227632, answer score: 3