Getting error "Annotation Query Failed e is undefined" on one dashboard

Since I upgraded my Grafana to v8 (8.1.5 at the moment) one of my dashboards gives the error toast popup below every time it is loaded and then also periodically when it refreshes.

Annotation Query Failed
e is undefined

If I open dashboard settings and select Annotations there are none apart from the Built-in "Annotation & Alerts that you can’t delete.

So does anyone know why I might get this error and how to stop it?

When I looked at the browser console I can see:

AnnotationSrv.query error TypeError: e is undefined
    j rangeutil.ts:269
    y annotations_srv.ts:236
    getGlobalAnnotations annotations_srv.ts:157
    getAnnotations annotations_srv.ts:88

Server and client are both on Ubuntu 21.04 and Firefox 93.0

The Dashboard has:
1x Stat panel
1x Statusmap panel
1x Table (old) panel