After days of testing on my own time, it turns out that the Turbotax form for MA cannot handle more than 99 entries on a given transaction report (I'm guessing it's the same for any type of transaction on the Federal Schedule D, like stocks, bonds, cryptocurrency, personal items, etc.). As soon as I add a 100th entry to a list of transactions, this error appears. Anything less than that does not trigger an error during review checking.
It seems like the only working solution is to split any report into multiple, separate uploads of 99 or fewer lines on the Federal return (which would involve manually editing one CSV into two or more). I can't imagine how an issue like this makes its way into a "final" software version, while we're paying to use and fix a broken program.
