I've seen them very rarely before, but today ~1 out of 50 requests results in a mediawiki API error:
Exception("{u\'info\': u\'The authorization headers in your request are not valid: Nonce already used: 145531318178372694281437064392\', u\'*\': u\'See https://zh.wikipedia.org/w/api.php for API usage\', u\'code\': u\'mwoauth-invalid-authorization\'}",)
crosswatch should catch these and try again.