WhatsApp for Xperia 5 II

This is almost always STAMINA mode or battery optimization restricting WhatsApp in the background while the screen is off. Open Settings > Apps > WhatsApp > App battery usage and set it to Unrestricted, then go to Settings > Battery > STAMINA mode and turn it off (or leave it off while you test). Also confirm WhatsApp's notifications are allowed to override Do Not Disturb under Settings > Apps > WhatsApp > Notifications. See how others solved this on Reddit

Sony's aggressive battery optimization is the usual culprit, so set Settings > Apps > WhatsApp > App battery usage to Unrestricted. Then make sure background data and unrestricted data usage are both allowed for WhatsApp under Settings > Apps > WhatsApp > Mobile data & Wi-Fi, and confirm STAMINA mode isn't auto-closing the app. After changing these, fully restart the phone so the notification service rebinds. See how others solved this on Reddit

Yes. WhatsApp manages this through Android notification channels rather than the system sound menu. Open WhatsApp > Settings > Notifications and tap the Notification tone under Messages or Groups, or go to Settings > Apps > WhatsApp > Notifications > Messages > Sound to pick any tone, including a custom file you've placed in your phone's Notifications folder. Per-chat tones are set inside the individual chat via the contact name > Custom notifications. See how others solved this on Reddit

No. Unlike older Xperia models, the Xperia 5 II has no physical notification LED, so there is no blinking-light setting to enable for WhatsApp. For an at-a-glance visual alert, rely instead on lock-screen notifications or turn on Ambient display under Settings > Display > Lock screen so messages show on the screen, and keep WhatsApp's notification channel and badges enabled under Settings > Apps > WhatsApp > Notifications. See how others solved this on Reddit

Long-term owners report that Sony's memory management closes background apps aggressively, which forces WhatsApp to reload and can drop notifications. Set WhatsApp to Unrestricted under Settings > Apps > WhatsApp > App battery usage, turn off STAMINA mode, and clear the WhatsApp cache via Settings > Apps > WhatsApp > Storage > Clear cache. Keeping the system and WhatsApp updated and doing an occasional reboot keeps performance stable over time. See how others solved this on Reddit

Early Xperia 5 II units shipped with notification and connectivity quirks that were largely resolved in later software updates, so first install all updates via Settings > System > Software update. For WhatsApp specifically, set it to Unrestricted under Settings > Apps > WhatsApp > App battery usage and re-grant Microphone, Camera, and Files permissions under Settings > Apps > WhatsApp > Permissions if calls or media fail. If problems persist, reinstalling WhatsApp after a Google Drive chat backup usually clears the corrupted state. See how others solved this on Reddit