For some reason cards from Commander Legends with a mana cost of 0 seem to be treated as though they have a mana value (converted mana cost) of 1 instead. For example, Jeweled Lotus is being grouped with 1 mana value cards when sorting by mana value. Not sure if this is happening with other recent sets as they don't tend to print a lot of 0 mana cards.
Additionally, modal dual face cards (MDFCs) like Birgi, God of Storytelling don't have a mana cost included at all, which causes them to be sorted as if their cost is 0, and affects the statistics of the deck such as mana symbol percentages and average mana value. This issue has also existed with split cards such as Life // Death for quite a while.
I don't know how easy these issues are to fix but thanks for all the good work you do!