Jira Software Server Plugin board sidebar is grayed out

I have created my web-item and web-panel as such, following the tutorial for the “project-centric view”:

<!-- Sidebar Item -->
    <web-item name="boardInsight" key="board-insight" section="jira.project.sidebar.plugins.navigation" weight="300">
        <description key="board-insight.description"/>
        <label key="board-insight.label"/>
        <param name="iconClass" value="aui-icon-large aui-iconfont-devtools-branch"/>
        <link linkId="board-insight-link">/projects/$pathEncodedProjectKey?selectedItem=${project.groupId}.${project.artifactId}:board-insight&amp;selectedBoardId=$selectedBoardId</link>
        <!--<context-provider class="com.optimahcs.sourceinsight.plugin.api.SourceInsightContextProvider"/>-->
    <!-- Sidebar Panel -->
    <web-panel name="Board Insight Panel" key="board-insight-key" location="${project.groupId}.${project.artifactId}:board-insight" weight="1000">
        <resource name="view" type="velocity"><![CDATA[<iframe style="border: none; width: 100%; height: calc(100vh - 100px);" src="/jira/rest/teamcity/1.0/resources/index?selectedBoardId=$selectedBoardId" />]]></resource>
        <description key="board-insight-panel.description">The Board Insight Panel Plugin</description>

However, when I open the tab (which works), the entire sidebar is gray, as if it were still loading.

How can I get the sidebar to load correctly?

presumably you have errors in your application log or your browser console. you need to look at these.

There’s no errors logging in either of these places. The only errors I am receiving are a few when running atlas-mvn package: Found a type [com.atlassian.plugin.spring.scanner.annotation.imports.StashImport] annotated as a component, but the type is not a concrete class. NOT adding to index file!! . I can’t figure out what’s causing those, but everything else about the plugin works except the sidebar disappears when I click my icon.

I got it working by loading in an HTML file with the resource tag, instead of using CDATA