Cubase Saved Mono Audio File As Stereo

Weird one this. It’s been asked before but the fix didn’t work for me.

At some point in the not to distant past all of the mono audio files in a number of my projects have been saved as stereo. It’s only the .aiff files, the .wav files are still in mono, and more recent .aiff files are still in their original format, mono or some in stereo.

This might be the system itself or it might be Cubase. It certainly isn’t me imagining it, I’ve already asked myself that question.

Any ideas please?