I'm trying to append the symbols I'm currently invested in, into the coarse universe function.  The reason being I want to ensure these symbol (that I'm invested in) are anayzled in my onData section.  I have a few indicators I'm using to determine exit conditions and need updated stock info onData.  

How come the following coasre function doesn't add my invested stocks back properly?

 def CoarseSelectionFunction(self, coarse): 
        sortedByDollarVolume = sorted(coarse, key=lambda c: c.DollarVolume, reverse=True)
        stocks = [x.Symbol for x in sortedByDollarVolume if x.Price > 15 and x.DollarVolume >= 900000 and x.HasFundamentalData == True] 

        invested = [ x.Symbol for x in self.Portfolio.Values if x.Invested ]

        stocks = invested + stocks
        
        return stocks[:self.coarse_amount]