Advancements reset after autosave

I was playing when the power went out. When I opened the world (which was autosaved), something weird happened: I was suddnely given advancements which I previously already had (like Stone Age and Cover me in Diamonds). Then I realized that other advancements that I had were gone. It's like if the advancements collected were suddenly reset. I don't understand why this happened, everything else was saved correctly, but I don't have my advancements anymore.