I’ve been having the same problem lately on my local development sites. This has been going on for a couple months.
I am unable to update on .test domains even though I see them in my “Manage Activations”. It even shows a sensible “Modified” datetime, ie: 2018-08-18 18:24:34.
I am able to update my live versions, ie.: domain.com
But whenever I try and update my local version, ie.: domain.test; I am getting the “Automatic update is unavailable for this plugin.”
I’m even updating the License Key locally and I am still unable to update.