Error: Invalid interval string

As of Grafana 8.1.5 / Pometheus data source, one panel in a dashboard (being a copy of another one within the same dashboard, but with a different {…} selector) is not displaying its content. The reason seems to be a BLANK interval value being processed as a non-empty value.

I re-created the panel, it doesn’t help in the long term, looks like subsequent modifications of the dashboard introduce the same error again.

A similar behavior was already seen in 7.0 as described here