Service item is missing after save PO

HI Gurus,

We met a strange issue.

When convert service PR to PO, service item is OK, same as in PR, but after save, in display ME23N or change ME22N,  service item is missing. Seems it is not saved.

Create

Display after save.

I believe it maybe caused by enhancement. Could you please suggest how to find the root cause?

For example, how to debug the program, in which program the service item is saved?

Thank you.

Richard