So I’ve messed about with the filterable condition a bit now too.
I tried matching it on the Id field of the 2 objects, rather than the object itself. No luck.
Then I tried the Id again, but setting it to a specific value.
On the inactive model condition I set the value to “” and then, on the button click I set it to {{$Model.Appraisal.data.0.Appraisee__r.Id}}
AND THIS WORKED!
Thanks for both of your help.