The Neltharion’s Call to Chaos (presumably BIS trinket from the Season 2 - current raid) does not show up in the “Special Items” list under the Customize option in the Addon site. The program appears to ignore this trinket that is listed as S tier on all the expert sites.
I’ll look into why it is filtered out of the list of customizable items. It is available and being ranked though.
For which spec do you think it should be ranking higher than it is?
For me as a BM Hunter it should be bis, but best in backs changes it for a 424 erupting spear fragment, and it doens’t show up in upgradefinder at all neither for hc nor mythic