Hello! New here.

I need to get a universe of equities that were trading in early 2015 for a backtest and view the tickers. (I need the tickers in order to pull data from an external data source.)   Whenever I backtest, I get a warning note that says "

Data for symbol PDLI has been limited due to numerical precision issues in the factor file. The starting date has been set to 12/30/2050" Sometimes the dates are less ridiculous but always not within my set time period. Is there a way to check if it was in fact possible to purchase PDLI in 2015, before adding it?

Also, I just added two lines of code and suddenly my backtest is taking ages. Any resources on avoiding that, would be appreciated.  Here are the two lines that seem to be making it take forever:
all_symbols = [ x.Value for x in self.Portfolio.Keys ]
self.Log("all: " + str(all_symbols))