To answer the question posted, I can only provide some details that led to it clearing on its own. It's important to understand that out of 400+ item rows, only 1 contained an error, line #246.
The problem was a calculated column named "RWDTotalActual" was returning a value of -428738486 while summing five similar calculated columns "RWDPeriod1, RWDPeriod2...RWDPeriod5, using the following formula:
Each of the RWDPeriod_ columns contain a formula to arrive at the number of days between an RWD1Start and RWD1Return column (respective of each period 1-5). The formula in these columns is:
Working backwards, I started with the RWD5Start/RWD5Return columns and reentered their respective dates recorded. Completing this action returned the same value to the RWDPeriod5 column, which in return, cleared the incorrect value "-428738486" being shown in the RWDTotalActual column.
I'm not sure why this worked, considering the data was exactly the same. Note also that there were more than 400 line items in this list, and only one item (#246) had this issue. All other rows (list items) above and below were calculated correctly.