The 26 Grammes Argent Pontificium Institutum Biblicum items has potentiall bad data on it.
I have some and they are 25.6 grams and apparently only sterling silver rather than fine .999 silver. Those are my measurements.
It's not a system/software bug if the wrong data was entered for these items. Post this in the Exonumia forum https://en.numista.com/forum/forum37.html or better yet just submit a change request directly.