My form being flagged for dates of stock being sold and bought even though dates are within boundaries flagged in red, why?

The issue has been submitted and is currently under investigation.  To fix this, please manually enter your "Date acquired" info. You’ll then be able to continue through your return.  We are currently working to resolve this issue.  If you would like to receive an update for the progress, click on the following link to get notified:

Acquired date

The acquired date is important to define if the transaction is considered as long term or short term.  Any asset you hold for one year or less at the time of sale is considered “short term” by the IRS.  Capital assets that you hold for more than one year and then sell are classified as long-term on Schedule D and Form 8949. 

If the date sold is "AFTER" Dec 31, 2020 then that's why it's being flagged. You won't report the sale on your 2020 tax return. It gets reported on your 2021 tax return which you'll complete next year.