Ever since installing this mod, achievements I've already acquired pop up again, every time I load any save file.

When I disable the mod, reboot the game and load any save file, this does not happen.

This is the only mod I'm using (and the only mod I ever used), so I'm inclined to think this is being caused by this mod?

This mod doesn't do anything with achievements, so I'm not sure why you're having this issue.

I can tell you however, as a modder I am constantly restarting the game and loading into new or existing worlds. Because the game keeps track of modded achievements separately from vanilla, mine get constantly fucked up, and I get new achievements all the time despite having them already, and I have no idea how to fix it.

I wish I could be of more use, sorry!

Thanks for your reply. Your comment about how achievements for modded games are stored separately lead me to inspect how that is happening. I found posts describing a file called "achievements-modded.dat" That file seems to be missing on my computer. Logically, without that file, Factorio seems unable to save achievement progress for modded games, which makes the achievements pop up every time. I'm asking around how to further resolve this. If I find a solution I'll let you know.

The confusing thing to me, is why that file is missing, and why Factorio isn't programmed to create a fresh copy of the file, if it cannot find it.

The Steam Cloud save storage was full for Factorio. For some reason this prevented factorio from making the achievements-modded.dat. You'd think that regardless of space on the cloud, the file would be made locally (plenty of room on my drive) but nope! After clearing the cloud storage, the game was able to make the dat file and started tracking achievements properly.

Wow, I never would have suspected that. Glad you figured it out, and good to know!