Every now and then, my ship will blow up at full health for no apparent reason. I wouldn't mind so much if the game gave me some kind of message about why, but I still have no idea what's going on.

It's very rare, which is why it seems odd (like it's not a normal mechanic). When it happens, it's usually in combat (against normal ships, not heroes), but I also died at least once in friendly space near a friendly station with no visible enemies around. I had just sent out a scavenger swarm to a derelict when my ship lit up and I'm sitting at the loading screen.

Is it cloaked enemies (or heroes) firing heavies, maybe? Is hacking a potential culprit?

I had that as well.

For me it just changed the way I play, no long journeys through space without docking (saving) a few times in between. It just wasn't worth it travelling 20min, just to be blown up after 18min.

Thanks. I'm playing with the latest Gog patch, though I upgraded to it in the middle of the campaign.

It doesn't matter when you upgraded. Fixes were implemented and content (if you have DLC) is not meant to be played before 38+ level. DLC storyline should be played upon finishing the main campaign. :)