Someone in the forums is now experiencing this same problem. I could not do as Stephen suggested - it would not save with no new monetary data, just an adjustment code. So I went into DB and did this:
UPDATE form_encounter set stmt_count =0 WHERE stmt_count = 2 ORDER BY id DESC
We will see on Monday if that worked for posting - billers have been unable to update EOBs received for 2 months! When I go into Patients dashboard, now they show insurance due amount correctly.