"However even then, some dividend reinvestment transactions are not included in the calculation."This has been discussed many times in here, and not seeing the dividend reinvestment transactions, while confusing, is perfectly fine for the calculation itself. The calculation depends on cash flows for each day in the period specified and a dividend reinvestment has both an outflow (dividend) and inflow (buy) on the same day, effectively making the net cash for for that day $0. If the security in question has only ReinDiv transactions the you won't see anything in the Investment Performance report that makes it clear that the security is being included. To make that conclusion you have to look at the composition of the beginning and ending balances. Maybe that's what you're seeing here?
Nope, the missing transactions are all buys, sells or cash dividends. As I mentioned in an earlier comment, everything appears correctly when sorted by security but some data gets suppressed when sorted by account or a time criterion.
Thanks for the insight provided in replies to my original post. I have taken a closer look at the types of transactions included with the different sorting criteria, and realized that everything is being taken into account correctly. I discovered that certain transaction types such as buys, sells, interest and cash dividend income are not itemized when the report is sorted by account. Adds, removes and return of capital always appear regardless how the report is sorted. This now makes sense - unless cash or securities are transferred in or out of the account as part of a transaction, the IRR doesn't change at the account level because the timing of those transactions is not significant for IRR calculation and the value just remains in the account ending total amount regardless what form it is in. However those transactions do appear when summarized by security because they have to be considered in IRR at the individual security level. The reason that some securities were disappearing from my report when it was sorted by account is that those securities only had buy, sell and/or dividend transactions. It's a confusing situation and I am feeling greatly relieved now that it's resolved!