Portfolio prices are wrong

I have noticed that the prices of the stocks in my portfolio are wrong most of the time.  They do change, and sometimes are correct, but mostly they are just plain wrong.  It seems that there is a problem and they do not update and persistently show the price as it was premarket.  Even though it showed the correct price at some point earlier during the day, it reverts back to the premarket price and does not reflect anything close to current price.