WSPR WARNING Return code -11

[waterwin]

2022-10-04 19:00:00,338 WARNING 1 [QW-1] decoder return code: -11 2022-10-04 19:00:00,419 WARNING 1 [QW-0] decoder return code: -11 2022-10-04 19:00:00,488 WARNING 1 [QW-2] decoder return code: -11 2022-10-04 19:00:00,591 WARNING 1 [QW-1] decoder return code: -11 2022-10-04 19:02:00,351 WARNING 1 [QW-1] decoder return code: -11 2022-10-04 19:02:00,391 WARNING 1 [QW-0] decoder return code: -11 2022-10-04 19:02:00,459 WARNING 1 [QW-2] decoder return code: -11 2022-10-04 19:02:00,661 WARNING 1 [QW-1] decoder return code: -11

What could be the reason for this behavior ? FT8 decoded fine.