Pretty low impact bug, but I've had some trade partners give me the side-eye for this. Fully charged (3 charges) requiem mods with 3 charges available will show as "[Requiem] Rank 0" in the trade confirm screen. I haven't traded requiem mods that are lower than Rank 3, but I'd presume that it always shows as Rank 0 regardless.
Fully reproducible, happens every time. Maybe Requiem mods simply don't have a rank, and the charges are unrelated to the rank system?