This is what Gecko wrote me back today:

Thank you for sending in this information. It appears that our data
provider has giving incorrect data as listed in your report. We also
found several other online sources showing these same inconsistencies.
We then went to the ICE website to check their daily values and only
then did we find that our data was inconsistent with the exchange. We
are looking into this and will contact our data provider to find the
source of the problem. Thank you again for bringing this to our attention.

So there you go. It was their boo-boo.

Erich