My guitar's pitch is different than tutor's using Zoom?

Hi there,

I've started getting lessons using Zoom on my cell/mobile phone and a Zoom H1 Handy Recorder. All is well, except our guitars, despite being tuned to concert pitch, are not in tune with each other by a full tone!

What could the problem possibly be? Tutor says it's only me that has this problem, not any other students.

If I send my tutor a recording, there's no problem. Only happens during live lessons.

The setting on the mobile App that I've switched on/off is 'enable original sound', but it makes no difference to pitch.

Thanks!

Brian, Ireland.