We checked this again - and that`s the problem with your connection interrupting, thus loosing connection to the server. This is responsible for all the problems, including ending quests that you are having.
The only two things to try are:
1) Restart your router/modem - turn power off and on.
2) When playing DoF - close any other applications running - any browser windows e.t.c
Aside from that the only thing that might help is logging out to the main menu, and logging back in every 30-60 minutes, to make sure no progress is lost.