Performance Management is generating Threshold Events that are missing from Spectrum via the integration.
Not all Events are missing, only some, in this case for Disk/Partition Items.
With the latest Spectrum r10.4.x release in development system the same problem is not present.
Performance Management r3.7.14
Unable to validate specific cause to tie to this issue.
Upgrade to the latest Spectrum release to take advantage of numerous defect fixes for the Performance Management<->Spectrum Integration.