Did you get any traction with your SR?
I get "no matching element" errors too. I have see issues where having two connected VIservers cause similar issues with tags as well. I can now get "Sequence contains no matching element" on my second command of the session. I will add that this same command work in an old virtual center in the same powercli session, and that a tag is indeed assigned to that datastore. The odd part is powerCLI is how all the tags got set in the first place when I built out this new vCenter.
[1]: Connect-VIServer vcenter.fqdn # Logon as THE vsphere.local\administrator
[2]: Get-TagAssignment -Entity (get-datastore NameofaSingleDatastore)
Get-TagAssignment : 9/22/2017 11:14:20 AM Get-TagAssignment Sequence contains no matching element
At line:1 char:1
+ Get-TagAssignment -Entity (get-datastore NameofaSingleDatastore)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [Get-TagAssignment], CisException
+ FullyQualifiedErrorId : VMware.VimAutomation.ViCore.Impl.V1.Service.Tagging.Cis.TaggingServiceCisImpl.GetTagAssi
gnment.Error,VMware.VimAutomation.ViCore.Cmdlets.Commands.Tagging.GetTagAssignment
VCSA 6.5.0.10000 build 5973321
PowerCLI Version
----------------
VMware PowerCLI 6.5.1 build 5377412
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Component Versions
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VMware Cis Core PowerCLI Component 6.5 build 6230110
VMware VimAutomation Core PowerCLI Component 6.5 build 6234650
VMware Vds PowerCLI Component 6.5 build 5374428
VMware Cloud PowerCLI Component 6.5 build 5375799
VMware HA PowerCLI Component 6.0 build 5314477
VMware HorizonView PowerCLI Component 7.1.0 build 5307191
VMware Licensing PowerCLI Component 6.5 build 5375648
VMware PCloud PowerCLI Component 6.5 build 5376282
VMware SRM PowerCLI Component 6.5 build 5374694
VMware Storage PowerCLI Component 6.5 build 5374001
VMware vROps PowerCLI Component 6.5 build 5375723
VMware vSphere Update Manager PowerCLI 6.6 build 5301639