Deleted Steam achievements (via Settings) restored and merged with new ones (2.1 Experimental)

[steelAgony]

Before starting a new playthrough on the 2.1 experimental branch, I deleted my Steam achievements using the game's built-in feature (Settings > Other settings > Delete achievements) to make the game feel fresh.

At around ~100 hours of playtime, the old achievements were restored and merged with the new ones.

Is there a way to fix this?
It's not a critical issue, but it somewhat ruined the pleasant experience of the new run.

[Rseding91]

Did you load a previous save file where you had completed the achievements?

[steelAgony]

No, I didn't. Before starting this new playthrough, I deleted all my old save files to ensure a completely fresh start. The only things I kept were some old blueprint books.

[steelAgony]

Just to give you the full picture:
I play on the 2.1 experimental branch on my desktop, and this new run is strictly vanilla Factorio: Space Age with no mods installed.

I also have a laptop with the main 2.0.7 branch installed, but I haven't played Factorio on it since I started this new run. I checked the client on my laptop—Steam Cloud sync is enabled, and there are no old save files there either.