p:dialog typeerror-pf-is-undefined when trying to show using widgetvar

Question

I am trying to show a dialog from either the web page, or from the bean. In either case it gives the above error and doesn't seem to be able to find the component in PF. I'm using PrimeFaces 5.2, and I don't seem to have the multiple version issue that was discussed here

I have pasted the relevant xhtml code below - the exact same behaviour occurs when I try to call it from the bean with:

RequestContext.getCurrentInstance().execute("PF('dlgTask').show();");

    <ui:composition template="template-restricted.xhtml">
        <ui:define name="body_content">
                <div id="title" class="sl-title">#{text['project.title']}   </div>
                <p:dialog
                    id="taskDialog"
                    widgetVar="dlgTask" 
                    modal="true"
                    closeOnEscape="true">
                <h:form id="taskDialogForm">
                    <p:panelGrid columns="1" layout="grid">
                        <p:outputLabel for="taskName" value="#{text['name']}" />
                        <p:inputText 
                            id="taskName" 
                            value="#{editProject.editTask.name}" />
                    </p:panelGrid>
                </h:form>
                </p:dialog>
                <p:commandButton      
                    title="#{text['project.task.new']}"
                    disabled="#{not editProject.canEditProject}"
                    action="#{editProject.createNewTask}"
                    process="@form"
                    update="@form"
                    oncomplete="PF('dlgTask').show();"
                    icon="fa fa-plus" />

Answer 1

This was caused by unrelated javascript in a menu section which declared a jquery.js library. When I removed the offending import, all of the strange Primefaces errors went away. It seems declaring other jquery libraries interferes with Primefaces code.