How to troubleshoot Bdocs that are in a hanged state in SMW01

Hello,

Some of my outgoind Bdocs (BUPA_MAIN) are in yellow status and the Bdoc state description says "Sent to receivers (not all have responded)". How do i troubleshoot this.

Nothing is visible in SMQ1/Q2 in ECC or CRM. Also I could not find anything in SMW01, ST22 or SLG1.

Can someone suggest how to troubleshoot such a Bdoc.

Thanks

Rgds

Priyanka