I've followed the documentation for creating a SSH Key on Mac through SourceTree (using my default one didn't work), and adding to my BitBucket personal settings.
This is from a repo I began on Bitbucket and used the integrated Clone feature (SSH link).
It works fine for a day or so then eventually is rejected.
Following the final suggestion to delete key and recreate and connect a new one from scratch of course works.
What's going on here and how can I get the key to stick?