We use multiple Jenkins versions (as noted in the environment) to boot VMs on a single vCenter for running builds.

The vCenter admins noted that the VMware vCenter would receive loads and loads of connections from Jenkins instances ... and the sessions never terminated / closed.

I have attempted a fix to this which can be viewed here:
https://github.com/ParagDoke/vsphere-cloud-plugin/compare/disconnect-vsphere?expand=1

Disclaimer: I'm a Java noob and have no insight into Jenkins model / functioning (let alone code). Please review with highest caution .

For now, we have asked our vCenter admins to upload a locally built hpi. Yet to hear about the results.