The deviation marker on a change order means that the status of the subcontractor cost differs from the status of the corresponding client income — for example, the cost to the subcontractor is approved, while the claim to the client is still not approved (or vice versa).
This is an informative warning, not necessarily an error — it makes you aware that the two sides of the change order are not in the same phase, so you can check whether this is intentional or whether something should be updated.