Hi,

For posting lines with CSS TYPE: EAM, a CSS posting will not to be created.

CSS type will be set as EAM for all other scenarios except if the connected customer of the work order is an external customer or if the work order is connected to a project and the project in turn is connected to a sales contract in IFS/Contract Management.

You have mentioned that in a particular WO, you have only some lines as EAM, and the rest as posted. One possibility of having few EAM lines while others as posted is due to the reason that,  you may have added the customer only after creating these postings  and not at the beginning of creating the work order. In such cases CSS Type-EAM will not get changed back to either Not Posted or Posted thus no CSS postings get created and this is how it is designed to work.  

Please check from the created date of the postings and you may be able to get an idea. Hope this helps to understand.

@Ash1807 

And EAM stands for Enterprise Asset Management, so als in IFS speak.