We have been experiencing this issue for quite a while.
Essentially, adding and deleting dvportgroups on our dvswitch (Distributed Virtual Switch) will work fine for hours... and then the next one will hang... the task will remain "In Progress" in vCenter for hours on end. Any subsequent attempts to add or delete dvportgroups will hang "In Progress" as well. The only way to clear these is to reset the vCenter service. Once reset, the existing jobs obviously fail and we are able to perform adds/deletes again until the next hang.
This issue causes problems with Lab Manager.. Lab Manager creates and destroys virtual port groups when configurations are deployed. However, this is not confined to Lab Manager generated tasks... When the conditions are right, I have been able to reproduce manually by adding/deleting dvportgroups in vCenter.
I've got a case logged on this SR#1525740521, and it has been escalated, but it has been open for a month or so and I haven't seen any relief. I have to reset vCenter on a regular basis.
IMMat - did you ever resolve this issue? We are experiencing something similar with regards to Lab Manager deploy/undeploy operations occasionally hanging and subsequently failing after exceeding their 900s or so timeout. Given that a deploy technically also creates a switch for the configuration I am wondering if this is the same thing.