I'm new here & still learning the platform (very slowly).

I understand that prices are supposed to be adjusted for splits & dividends by default, but I'm getting an error on a simple buy-and-hold test for etf symbol TQQQ with a basic template algorithm.  The 2:1 split in Jan2017 appears as ~50% drop instead of a split.  (Stockplot shows the same drop).  Am I doing something wrong?  Is there a way to confirm the data integrity & fix if necessary?