This is within the scope of normal LiveO2 experiences. When the oxygen saturation drops during the training session this is a detox event. In other words, a portion of your body’s micro-circulation is opening an area that has been closed off. This is a good sign that you are positively affecting the micro-circulation switching mechanism and is also very common during the 15 minute protocol. When this happens for the first few times about half of individuals notice a smell they do not consider normal for them. It can come in the form of smelly sweat, breath, urine, bowel movements etc. It is your system detoxing and it is hard to say what exactly it is, but the important thing to keep in mind is that it is leaving your body. Most experience this once or twice and then it goes away or becomes less intense and eventually clears.
The video here mentions this around the 2:30 time mark. It is a pretty good explanation of what is happening in your tissues and detox tides.