Phantom Filter: visualisation indicates filter/slicers is applied; but no such filter/slicer exists

I have a tab with a 'Slicer' and a 'Table'  both showing the 'Fiscal Year' field from a DateKey table.

Both visuals display a partial list of the 'Fiscal Year' values defined in the table. Adding (by copy/paste) the same visual to another tab shows the correct full list. Removing and recreating the visual on this tab shows a 'filtered' list. Changing the visual type between types (slicer/table/multi-line card etc.) does not change the results.

When hovering over the filter icon in the top-rigth the pop-up indicates a Filter is affecting this visual. The mystery is that there are no filters or slicers defined.

At one point in the life of this report/dashboard there were 'Synced Slicers' in play, but these have all been removed or deactivated. It really feels like there is one still active but I can't find it.

The same behaviour is evident on each of 3 tabs that were duplicated from an original.

Closing and opening the files; refreshing the data have all NOT helped.

Any ideas or suggestions much appreciated.

Paul