save games are always a problem, even when you follow all the rules, you could still have issues.
first, before you start a campaign, you have to make sure you have a stable, CTD free mod instal, then, ideally, make no changes to your mods or game options during the campaign.
second, there are threads on "rules" to follow when saving. I always save surfaced, on the NAV map, with the game paused and ideally with no land or ships in the area.
I also save every 12 hours, at least, so that if any issues do crop, I have issue free saves I can go back to.
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