The card Cinderslash Ravager says:
"At the beginning of your turn: if this card is in your hand: Reduce this card's cost by X until end of turn. X is the total Oil Counter value among cards you control."
"Cards you control" should include your supports that have Oil Counter, however, in practice (tested in Training Grounds and against Fblthp), Cinderslash Ravager is only reducing its cost by an amount equal to the total Oil Counter value on your creatures, and is not counting the Oil Counters on your supports.
This seems like a pretty straightforward bug to me so hopefully it's an easy fix!
Thank you for all the information provided, this issue will be investigated!
If you have any additional information that you consider relevant, please don't hesitate to send me 😊