Hello,
Please refer SAP KBA,
1935025 - How to change the message type of message RU442
You have to specify in the parameters for the order confirmation (OPK4) that the activity sequence is supposed to be checked. In that operation sequence set as Warring/information when operation sequence is not adhered to.
During milestone confirmation always previous opeartions will be confirmed they why are you confirming previous operation manually.
Best Regards,
R.Brahmankar