Update: it happened again while testing some more. I just changed some Wait durations, started the preview and tried to load the save game.
One was changed by +0.05 sec, another by -0.05 sec as I'm trying to adjust an animation timing with the SFX.
The Waits were unrelated to the load because they happen on an event that was triggered manually after the load.
This freeze seems to happen once every 30+ loads.
This time it's better though since there are errors