I loaded a Fulgora start save made with mod version 1.0.5 in the latest version (1.1.15) and it breaks something with the availability of planets.

When loaded in 1.1.15, I get a popup saying something about not being able to switch starting planets on existing saves (which I didn't attempt to do). It gave a warning about softlocks so that's what I'm calling this. From then on, Nauvis is the only planet visible to me. Fulgora is greyed out on the map even though I'm currently on it, and if I try going to my platform in orbit then Fulgora doesn't show up on the list of planets I can drop my player on.

When I backdated the mod to version 1.0.5 it fixed the issue. Interestingly, it also fixed the issue on autosaves created after I updated the mod to 1.1.15. Updating the mod again to test resulted in the same bug.

I wouldn't mind sticking to the old version for this save if I have to, though I was interested in using On Wayward Seas, which requires version 1.1.14 of this mod. Let me know if there's anything I can do to help, or if you'd like the save file!

I did some testing with different versions:

• At first glance, 1.1.12 works just as well as 1.0.5 and all versions with significant download count inbetween
• 1.1.14 gives the "Changing the planet mid-save" warning but doesn't appear to have broken the planet list in the same way as 1.1.15 does
  • After some more loading attempts, 1.1.14 causes the same bug
• 1.1.13 has the bug

I'll play with 1.1.12 for a bit to see if it creeps up, but it seems like it first appeared in 1.1.13. Fortunately it seems like the bug isn't permanent, and reverting versions fixes the visibility of Fulgora

That's not good. I haven't had any other reports about this happening, you're 100% sure the startup setting didn't get changed somehow?
I believe I did rename "nauvis" to "none" in the settings between then and now, but that shouldn't affect anything if you started on Fulgora.
You are trying to update from a 5 month old version of the mod after all, so while there ideally shouldn't be issues with that, I'm not surprised.

If that's not the case, feel free to send me the save on either my discord server (or the main Factorio server if the save is too large for mine), or if you're not on discord you can use a site like catbox.moe for easy filesharing.

I didn't modify the startup settings afaik. When I'm on a version where that popup appears, and I go to Esc > Mod settings > Startup > Any Planet Start, it still shows up as Fulgora. I didn't even know you could edit those tbh.

I did add some mods (namely dredgeworks and AAI signals/vehicles) before originally loading my save from 5 months ago, but the bug appears even when I sync mods with and load the 5mo old saves with up-to-date mod versions, so I don't think the new mods are causing issues.

Something potentially of note is that I'm on the native linux build. I tried it with proton on the windows build but the bug still appears (good job wube, even got bug parity! :D)

While loading between my saves from yesterday (played for a bit with mod version 1.1.12 with no issues):

• The "Changing the planet mid-save doesn't work" error does NOT appear if the nauvis tech has been researched already.
  • In this case, both Fulgora and Nauvis appear normally in the map's planet list
  • For this particular save, the timeline was:
    • Start game on fulgora with version 1.0.5
    • Update to 1.1.12
    • Research Nauvis tech
    • Updating to 1.1.15 no longer results in the bug
• The error DOES appear in the earlier save where the nauvis tech has not yet been researched.
  • In this case, only Nauvis appears on the map's planet list (despite me and my only platforms being on Fulgora)

There is a possibility that this is due to a quirk of playing with 1.1.12 in the meantime, and I don't wanna mislead you if that's the case. I think this difference is worth investigating though so I'll send both pre and post Nauvis tech saves to #general in your discord.

Pasting from Discord:
I figured out the issue, 1.0.5 I wasn't caching the planet setting anywhere but in more recent versions I am, so when it migrated from having nothing cached it was not equal to the setting value and the mod figured that it must be because the setting was changed, not that it didn't exist before. I just loaded the original 1.0.5 save with a fix and I'm not getting any warnings, and fulgora is still the only planet I have access to. thanks for the very detailed report, it was massively helpful! Fixed in 1.1.16