Game saves are seriously flawed, always have been. Ubisoft decided to just leave it that way. Here's some rules about game saves I d'loaded from SubSim a long time ago:
- Always save when surfaced.
- Always save when in control room, F2, view.
- Always save at least 50km off shore.
- Always give the game a little time at TCx1 after being on high TC before you save.
- Never save with any known contacts, go some 50km away from your last sinking.
- If the first save works, do not over write it. Make a new one which you may over write.
- If two convoys spawn close to your U-boat at about the same time, then any game save made afterwards, wherever saved, will be corrupt.
- Any game-save made after a convoy has spawned with Sergbuto's AI U-boats attached, will also be corrupt.
- Give the game a little time before you exit, just a couple of seconds of your time...
- Before saving, dive, turn your engines off, go to the hydrophones station, turn up the ambience volume knob and listen. If you hear a ship, don't save. Also, don't save if you're less than 50km away from land.
- The sound of broken glass at loading is the game setting your damage status from your last save point. Even if you have 99% hull integrity you will hear glass breaking. Is normal.
There's also something in the GWX documenttion about saving too close to harbors causing ships to crash and burn or very similar.