Gladly! 
Thanks for targeting this nasty bug closer. 
I don’t use LAN. (I haven’t even installed BONJOUR.)
The problem occurs in game mode: SINGLEPLAYER => CUSTOM CAMPAIGN…
I’ve created 5 custom campaigns.
| Name of the campaign |
Crash by trying to save? |
Download the campaign |
| Prologue campaign |
No |
https://www.eredalis.de/files/download/warcraft/Heroes00.zip |
| Human campaign |
Yes |
https://www.eredalis.de/files/download/warcraft/Heroes01.zip |
| Undead campaign |
Yes |
https://www.eredalis.de/files/download/warcraft/Heroes02.zip |
| Orc campaign |
Yes |
https://www.eredalis.de/files/download/warcraft/Heroes03.zip |
| Nightelf campaign |
Yes |
https://www.eredalis.de/files/download/warcraft/Heroes04.zip |
I’m using the presets for the races within the campaign editor.
For example (Human campaign):
TAB: GENERAL
Image (Minimap)
Preset: Human
TAB: LOADING SCREEN
Background Screen: Human
Cursor: Human
Ambient Sound: Human
ON A SIDE NOTE: Yesterday, after the release of Patch 23101, I created a new campaign file (.w3n) for testing purposes. I imported only all 10 maps from the human campaign, nothing of the additional stuff, like sounds, models, etc.
With this raw file, so to speak, I tried out this new campaign file by starting the first chapter, skipped the first cinematic with ESC and pressed F6 to save the game and - no crashes so far!
While you guys investigate this, I will continue to import the remaining data of the human campaign into the new campaign file, perhaps I will find a clue as to the point at which it becomes impossible to save the game.
Please let me know if I can provide you with anything else or more information. 
/edit: Ah, and by the way… The topic here above, the crash after return one step back in menu, this only happens when you have opened the main menu of one of the said 4 affected campaigns, which leads to a crash… So there must be a connection.
/edit²: New bug report regarding this issue here: The reason for the crashes in some custom campaigns?