Bully clutch not disengaging

It seems like a few times over the last two race weekends that one of the bully clutches (2 disc, 6 spring) that I have is failing to disengage when slowing down for a caution or the like. It will eventually disengage, but it seems to be very delayed. The stall speed is set correctly, if not a tad high. In my head, i'm thinking the levers are sticking, but is there anything else that would cause this?
 
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