when you stop the training to address that one individual, then you loose the rest of the group as they get having their own side conversations because they think "he isn't talking to me".
Yes. But acknowledging them and their issue and mentioning that it will be addressed after, shows the rest of the group you are thinking of them and valuing their time, whilst still catering to individual needs. You can also add that if anyone else comes across the issue (like missing student), that they should take note and "we" will look at it together after the session/ later date. It is generally an effective tool to give people the power that they feel they can concentrate on what is at hand and still have their concerns addressed.
Good point. Thanks again for that!