how to find out which key it tries to access?

Try running with

--debug

.

$ pulumi up --debug (emesa1-rename|✚1…) error: failed to load checkpoint: blob (code=NotFound): NoSuchKey: The specified key does not exist. status code: 404, request id: F32C7ED830E32CDC, host id: Q4eqyG5DxUpA9DTzIW0KTjgqiDykzEXo0xGt4WIathncaYs7I6NC99sojb42/qDtdJAFu2TJXxo=