Just compare the Image version between the failed unit and the succeed unit.
The default Agent version indicate that the ThinPro 5.2 image on the failed unit is released later than HPDM 4.6 SP4. I don't have a quick answer of which is the new features in this image might cause the failure, but we can't gurantee the old DM server can always support the newer image - especially it's Linux.
This is the major reason that we keep on releasing service pack - to fully support those new released operating system.
I guess there is some differences between the unit in differente sites, otherwise the issue will be too strange to us.