XRECOVER or XADVANCE for the specified session_id has encountered a volume pair (privol,secvol) that was in CPY or PND status at the time when mirroring was interrupted.
Processing continues, but the data on the specified secondary volume may be incomplete and/or inconsistent with other secondary volumes. Also, for XRECOVER, the secondary's volume serial number will not be clipped.
If it's unexpected for the session to contain a non-duplex volume at the time when mirroring is interrupted to produce a tertiary copy, you might need to recreate the copy at a time when all volumes are in duplex.
Extended remote copy (XRC).