Mining Grin on v13.1.0 produces this error often on the grin-server stratum server.
ERROR grin_servers::mining::stratumserver - (Server ID: 0) Failed to validate share at height 12748, hash 787314f9428c, edge_bits 29, nonce 23765210304776512, job_id 1. Err(Error { inner: Verification Error: endpoints don't match up })