I have found an issue with the solution but I feel like I should share this information to see if it can be reproduced by others.
I've been having this issue when I recently started playing again that some of my saves (I think all quicksaves) would not work in terms of loading the game.
One case of this was on coop where I was gelt and my friend was belegar, whenever we would continue a campaign, usually left on a quicksave battle, he would load no problem but for me;I would see the wrong background image (random, sometimes I would see a tomb king art instead of the gelt on a horse vs undead art) and it would not even take 5 seconds for the loading bar to finish and boot me back to the main menu
We would have to use an autosave of the end turn to circumvent it
I then later on had the same issue on my new singleplayer game as the last defenders, turn 13 quicksave
I load it in, booted to the main menu, I load quicksave of turn 11, booted to main menu, I then try it all the way back to turn 2 where it would just crash instead
If I tried to continue campaign via launcher (on that turn 13 quicksave), it would crash after 1 second of launching the game.
I asked my friend if he could load my quicksave, he could. So I knew it was not my save but me, so while I was busy finding out the issue, he was doing the battle for me for fun, he then finished the battle and send me the save file back ("saving my disaster battle"), I then noticed I somehow didn't have gortrek and felix installed (I thought I did this whole time) so I could load his save, I installed it after claiming it and I managed to load his save.
Not only that, I managed to load ALL of my quicksaves of the campaign I couldn't load 10 minutes ago now that I had that dlc installed
-Have quicksaves/saves(not sure about the save bit, quicksaves were consistently failing from my experience atleast)
-All dlc EXCEPT gortrek and felix installed
-Try to load your game