This sounds more and more like a player personality issue. Which is the worst type of problem to try to deal with... You have a very social, chatty player
And, there is really not much that you can do about this as some people are just naturally chatty and social, and you are effectively trying to get them to change who they are at their core, something many people the world over just can not do.
the only thing I can think of is change how you lay out your missions so there is no downtime for ANY of the players. Now that is easy to write, but hard to do in practice. But here is a few examples.
Have the combat characters do observational overwatch during the meet when the face is active. (they could be looking for clues to their Johnson's identity by his manner, his clothing, his style of speech. Keeping an eye open for betrayal or ambush, etc)
During the combat times, have the technomancer and Face provide the Overwatch (thechnomancer keeping an eye out for matrix problems, the Face for physical security or problems..)
anything to keep ALL members of the party doing something and feeling important.
which means, yes, you will have to change the way you structure some events... So now, there will HAVE to be a hiccup in the matrix for the technomancer to deal with, or an unscheduled patrol that the face will have to deal with (and this doesn't mean combat... could be talking to them, acting as 'eye candy', impersonating an exec that needs their help..... try to keep it to things the face can ACTUALLY succeed at.)
Ahhh, the joys of being the GM
