Sounds like a fletching clearance problem. Whiskerbiscuits can produce drag and interference, just look at it. Ditch the biscuit and get a good drop away restif you want cleaner more consistant flight. The whiskers wear over time, it is not a consistant rest. It is good enough for hunting in most situations. Biscuits have good points but tuning and accuracy over time it can vary. Offset vanes will contact more whiskers than straight fletch so it may tune differently.