There is one rare case in SAP PI when the message is successful in SAP PI but it actually failed in PI with its OUTBOUND STATUS in error.
As a SAP PI consultant I luckily faced this issue. Our ABAP team asked us for few IDOCs that were not reached to their system on one particular date. When we checked the IDOCs in PI for mentioned date, we found that those were successful but actually not.When we scrolled to right of the message entry we noticed the red flags which means not processed to target system.
We usually check the messages with the main STATUS which we see at very first column in SXMB_MONI window but it may not tell you the real story so OUTBOUND STATUS also play role.
Now I will discuss the issue with screenshot references.
At first we find the message entries with red error flags in OUTBOUND status
As we know the RFC calls of IDOCs happen through tRFC queue i.e. SM58. So we need to give a look for the erroneous entries in SM58 for the same failure date. Here in our case we found that calls for the same ABAP system were in error so we need to test the connection and if connection is OK we need to execute all entries.
These RFC calls (LUWs) need to be executed from SM58 but if they are many then do the Execute LUWs
So to execute all failed LUWs with below steps:
Goto Edit and Choose Execute LUWs
Enter the target system details in Destination and select the date as per date of failed entries. Select the check boxes as per error entries.