Mail messages tab in Translation job view remains empty


I have a Mail messages tab in the translator view, but it remains empty even if messages have actually been sent from that job. Also, as you can see all options are greyed out.

It works fine however in the Assignment (see below) and Translation projects views.

This is part of the layout tree

FYI, I use TBM v5.3.43.

Does anyone know how to solve this?