Template variables could not be initialised: undefined

I’ve just recently started using Grafana, and initially installed the version deployed with OpenNMS-Helm 2 which installed Grafana 5.1.4.

I was then having a look around in Grafana, and discovered the Azure monitor plugin.

I set up an Azure Monitor data source, and created a dasboard with a number of template variables where the query for each variable is dependant on all the previous variables:
Variable Definition
$datasource Grafana-azure-monitor-datasource
$ResourceGroup ResourceGroups()
$NameSpace NameSpaces($ResourceGroup)
$ResourceName ResourceNames($ResourceGroup, $NameSpace)
$MetricName MetricNames($ResourceGroup, $NameSpace, $ResourceName)

and I had a repeating panel that this was working for.

I found that the OpenNMS-Helm requirement was only a minimum version for Grafana of 5.1.4, so I upgraded my grafana instalation to 5.4.2 directly from the Grafana yum repository.

Now I cannot get the MetricName variable to work. For all the other variables, the “Preview of values” is displaying the expected set of values, but the MetricName variable, if I try and press the Update button, or select the “multi-value”, or “Include All option”, I get a toast popup saying “Template variables could not be initialised: undefined”

Is this an issue with the Azure monitor plugin and an incompatibility with the latest version of Grafana, a bug in Grafana, or a user error?