Sales Order is not editable in offline mode, including header fields, or add products. However, you found some fields are still editable in online mode.
SAP Cloud for Customer
The reason that the sales order is not editable in offline mode is because the order has the Status 'in process' (It is the designed behavior that the changeability in offline mode is more restricted than in online mode to ensure the consistency of the documents).
If the Status 'in process' was set by the ERP ( via the replication message). From the C4C point of view, the order is open ( whenever a new change was made in C4C, the status became Open. However once the change was replicated to the ERP ( occurs automatically ), the ERP sent the 'in process' again back to the C4C).
If this is not the wanted behaviour, you need to check the ERP side and do the wanted adjustment for the Status setting, to make the Status 'open' in C4C.
Sales Order, Offline , KBA , LOD-LE-CQP , Customer Quote Processing , Problem