When adjusting invoices in Accounts Receivables that have units, the units column for each invoice distribution will prefill with the total units billed on that line item.
You must remove or override the units column to be blank (no units being modified) or enter the number of units that should be reduced on every line item, even lines not being adjusted.
To find the Units column, scroll to the left until the Units column appears and remove the number from the Units column, or override the prefill with the correct number of units that need to be adjusted.
To correct existing adjustments, void the adjustment in Adjust Receivables and re-enter with the correct number in the Units column.