DooM 3 don't continues, stuck at level 18 :-(

Hello guys,

another (new) problem with my DooM 3 gog version. When I have finished Delta Labs - Level 3: Union Aerospace Research Division the game don't goes on to Delta Labs - Level 4. Instead it falls back/switches to the DooM 3 main menu ... ? The game itself is up-to-date and I don't know why this happens or what is wrong with the game. I retried the level two times and it happened both times the same mistake. Any ideas?

I played it the third time and it happens still the same as before. The game falls back to its main menu and I can't go any farther in the game.

Now I have played the 18 level the fourth time today and it is still the same problem. After entering the exit the loading screen for Delta Lab 4 shows up but I am getting prompted to the DooM 3 main menu.

Something seems to be wrong with my DooM 3 executable. Running the executable direct from its installation folder without the gog galaxy launcher front end changed nothing to the game too. I have tried one of the source ports dhewm3 and this worked even with my save game and I could carry on in the game.