Vocal levels different after audio export

Hi everyone
Would really appreciate some hep with this one! For some reason the vocal level is either too high or low after I export the audio. I have been pretty happy with the mix when played back in Cubase, and so have my clients. Playing it back after the file has been exported is a different matter.
Than you for your time

Are you using the Control Room? If so it’s possible to have two output signals going to your DA convertor>monitors. This can cause the mix to sound different on playback compared with the rendered file.

Playing it back on what? same system, same speakers through Cubase?