I'm getting an error message from the Perio.do client (v5.0.19). It's happening for a local in-browser (editable) data source. I have performed 'import changes' to bring in the Heritage Data periods list, with the objective of revising it - as Phil Carlisle at Historic England has recently added to and revised the published Linked Data periods list.
When I go to 'browse authorities' then click 'edit' on the only authority now listed in my data source, the following message is displayed:
As reported by Ceri Binding: