Exporting Stems in Mono

Hello

I have a very large session containing over 10 tracks. All but two files are in Mono within the session but when I export stems they switch to stereo. I need them in mono, can anyone help? (Beyond manually going through and saving them individually as mono, which is not an efficient work around given the amount of exports I need to do).

One thing I notice is that the channels options, to switch to mono, is greyed out...

Thanks,

Max