Not sure if it is a bug or if it is not implemented yet, but I noticed that while selecting the Drums (4-Lane Pro), it automatically converts any 5L chart into 4-Lane Pro; However, the same do not happen while selecting "Elite Drums" as an instrument.
#Elite Drums is not converting 5L charts like Pro Drums Do
prime sigil
tame swift
As of right now Elite Drums is not yet an actual gamemode. You can read in the #elite-drums channel about it's implementation, but charts are being made for it despite not being available for full play yet. The option for Elite Drums as an instrument is there because YARG does currently support automatically downcharting Elite Drums charts to Pro Drums.