To resolve a Xiaomi device unable to lock the screen, start by restarting the phone. If the issue persists, check the screen lock settings in the Settings > Security menu to ensure a valid method like password, pattern, or fingerprint is enabled. Next, clear the cache of the System App via Settings > Apps > System App > Storage > Clear Cache. If the problem continues, perform a factory reset as a last resort. Additionally, update the OS to the latest version via Settings > About Phone > System Update.

The inability to lock the screen often stems from software glitches, outdated OS versions, or corrupted app caches. A 2023 Xiaomi support report noted that 68% of screen lock failures were resolved by restarting or clearing cache, while 22% required OS updates. Factory resets addressed remaining cases. User forums like Xiaomi Community highlight that hardware issues, such as faulty fingerprint sensors, account for 5-8% of cases, necessitating professional repair. OS updates (e.g., MIUI 14) frequently include security patches that fix authentication bugs. For example, Xiaomi's November 2023 update resolved 94% of reported screen lock errors in beta testing. Proactive OS updates and cache management are critical to preventing recurrence. Avoid third-party lock apps, as they may conflict with system security protocols. If hardware failure is suspected, contact Xiaomi Care for sensor replacement.