Он спросил, что мы делали с тех пор

Он спросил, что мы делали с тех пор, как начали работать над этой проблемой

Результаты (английский) 1:

He asked what we were doing since started working on this problem

Результаты (английский) 2:

He asked what we were doing since they started working on this problem

Результаты (английский) 3:

He asked, what we have done since then, as have started to work on this problem