I've noticed this for few years, snf I finally asked Interactive Brokers: I purchased some shares after 4 pm close, but my average price, showed as not only above the high of the day, but above the high for the prior 2 months. I never thought my total equity was incorrect, but more just accounting errors. Sometimes I thought the average price was just a little off, perhaps reflecting commissions. But IB explained it: If one buys & sells a stock for a loss (apparently that day, or even prior 30-days,) IB automatically ignores the loss, due to IRS wash sale rules. I never would have guessed that was the explanation. I pointed out to them that I'm classified as a trader in stocks & stock options, so the wash sale does not apply. Apparently IB never considered that, nor provides any feature to ignore the wash sale trades. While this is annoying for day-to-day average prices, on IB annual summaries of trades, my accountant always has to manually adjust to include those losses in my IRS reporting.
I use IB's Gateway not TWS, but I had a similar problem where the AvgPrice in the Portfolio messages was far from the actual ExecutionPrice. I called IB, told them that I used Mark to Market, and they made some sort of entry in their database, and the problem never reoccurred.
Thanks; I'll try, although I told IB support that wash sales do not apply to my stock & option trading. But maybe for some reason TWS can't handle that, vs IB Gateway.