I am taking this one only because I use Vanguard as well and this is a 2020 Vanguard internal issue that they have encountered. You may still manually enter this information as the information Vanguard has submitted to the IRS is accurate.
If you have a plethora of transactions that you are trying to upload from Vanguard directly, you can still list on Schedule D in two separate transactions - totaling one for STG/<L> and another for LTG/<L> and that is acceptable by the IRS.
