Quicken sometimes updates security price history with wildly incorrect prices and trading volumes. This seems to happen when I open my Quicken data file, and the program attempts to download current prices for securities. Of the over 1300 securities in my portfolio, this happens to perhaps 10-20 securities when it does occur. I typically see incorrect prices in groups of 5 days. This has been happening from time to time over several years and releases. Today I exported the corrupt price histories to CSV files for 11 securities (including Wells Fargo, Microsoft, Comcast) and can share these with Quicken support if interested.
Windows 10, Quicken R64.30.