A cloud application uses clustered database servers for a large website. Users are reporting occasional trouble logging into the site. Logs show this only happens when users connect to one particular

User password expiration would affect all users attempting to log in, regardless of the specific database server they connect to, and would likely not reoccur precisely every three months after a reboot.

Server certificate expiration is a common issue that causes authentication failures for specific servers, especially if connections rely on TLS/SSL for security, which would affect user logins. The recurring nature of the problem every three months, fixed temporarily by a reboot, strongly suggests a certificate with a three-month validity period or a certificate that expires after a specific renewal cycle, as reboots often clear temporary cached states.

A database version mismatch would typically cause persistent and immediate issues across all relevant connections to that server, not temporary issues that reoccur after several months and are fixed by a reboot.

Time synchronization issues, while critical for clustered environments and authentication, usually lead to immediate and consistent authentication failures or cluster instability, not a temporary problem that reoccurs every three months on a single server.