this is a common problem to this engine and occurs if the water pump flange is mounted without beeing aligned (not centered). It has to be aligned with a special tool available from Volvo. If the tool is not available it may help to center the alignment by turning the engine by hand before tighting the bolts.
Mine got damaged due to mechanics in turkey removing it and not aligning it when putting it back.
I have to exchange the part that is mounted on the shaft next year, too.
SN 120 KALI MERA, Panama