It should be some other problem, the same have happened to me when I saved a game some minutes after survived to an attack to a convoy and sunked some ships. I used the "Save and Exit" option and in the next day when I loaded this saved game to continue playing, the game will load normaly but after a minute the game exited to the abandon career screen. I made several attempts and in one of them I hited the ESC key and select the option to end the patrol and return to base, which I was able to do, but for my suprise when I tried to start a new mission my career status was "Dead".
Maybe, some members of my crew didn't like my decision to sink some of the ships and have shooted me.:rotfl:
Anyway, since I had a game saved before attacking the convoy I was able to reload and attack the convoy again and continue with the mission without any problem. So, one lesson I learned is to save just before attacking a convoy, because I can allways reload this save game and do it again.
And by the way I don't even have those mods installed, only the mods about deck loading guns speed, SpySat, 16 Km and the better periscope.