I loaded a save near a wreck, where a gift used to be.
Now the gift is not visible anymore but a ghost monument scared me to death, waiting behind me.

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I guess this state is related to the save being generated while the gift is visible.
I saw the wreck before (there was no gift and no monument). Then I went by mistake into the water and I could not retrieve the vehicle, but I discovered that O2 is unlimited.
I loaded a previous save and I visited the wreck once more and the gift was visible and I made a save there.
Now the 10k heavy gift is invisible but a ghost monument stays above the wreck.