I’ve noticed this a couple of times while running with SM&M++. It’s ridiculously minor and very much an edge case, but I wouldn’t be doing my job if I didn’t mention it. Ships with variable loadouts can occasionally have different explosions between savefile loads. For example, the Snekke usually goes out with a blast explosion, but it’s possible sometimes for it to explode with thermo. It’s always consistent for all of a particular shiptype when you load a savefile, but loading the same savefile again can result in a different explosion each time. I’m guessing that the different explosions happen when the game picks a more violently exploding loadout for the ship during type initialization.
Does the ship have a defined level? If not, the game assigns a level equal to its highest level item. For example, Manticore with the level 7 mark V howitzer will explode bigger than one with up to level 6 weapons.
Default ship explosions vary by level, and level is determined by item level, if it was not explicitly defined, when the ship is created.
I think what's happening is that the explosion type is set at load time for a given ship class. If a ship class has a variable loadout, then depending on which combination the RNG picked, you get a different level of weapons/items. As PM says, that will cause a different explosion class.
I'll see if there is a way to make this deterministic. But I agree that it is low priority.