WhatsApp for Redmi Note 9

The proximity sensor is staying triggered, which is common on Redmi devices, often after a MIUI update. First make sure no screen protector or case covers the top of the screen near the earpiece, since that overlaps the sensor and keeps the display off. Then test the sensor: dial *#*#6484#*#* to open the hardware test menu and run the proximity check with nothing near the top of the phone. If the sensor reads wrong even uncovered, a software glitch is likely, so restart the phone and update both MIUI and WhatsApp. If it still misbehaves after that, the sensor may be faulty and need service. See how others solved this on Reddit

MIUI's aggressive battery management closes WhatsApp in the background, which drops the linked Web session. Go to Settings > Apps > Manage apps > WhatsApp, set Battery saver to No restrictions, and enable Autostart. Then open Recent apps, hold the WhatsApp card and tap the padlock to lock it. Keeping the app alive in the background keeps WhatsApp Web connected instead of repeatedly logging you out. See how others solved this on Reddit

The most common cause is that the voice note is playing through the quiet earpiece instead of the loudspeaker, because the proximity sensor thinks the phone is held to your ear. When you press play, keep your hand and any case away from the top of the screen so audio routes to the loudspeaker. If voice notes consistently route to the earpiece even when the phone is flat on a table, the proximity sensor is misreading, so test it via the *#*#6484#*#* hardware menu and update WhatsApp and MIUI. See how others solved this on Reddit

MIUI is killing WhatsApp before the incoming-call alert can fire. Open Settings > Apps > Manage apps > WhatsApp, enable Autostart and set Battery saver to No restrictions. Then under Notifications make sure Calls notifications are enabled with sound and pop-up allowed. With background activity and autostart permitted, the call alert arrives in real time instead of only showing up as a missed call afterwards. See how others solved this on Reddit

A MIUI update often resets background permissions for WhatsApp and can leave a stale cache. First go to Settings > Apps > Manage apps > WhatsApp > Clear data > Clear cache (do not pick Clear all data, which would log you out). Then re-enable Autostart and set Battery saver to No restrictions. If messages and calls still fail, update WhatsApp from the Play Store, since older builds can break on newer MIUI releases. See how others solved this on Reddit

Calls dropping to on-hold the moment they connect usually means WhatsApp is losing microphone or background access. Go to Settings > Apps > Manage apps > WhatsApp > Permissions and confirm Microphone and Phone are allowed, then set Battery saver to No restrictions and enable Autostart so the call isn't suspended. If it persists, clear WhatsApp's cache and toggle airplane mode off and on to reset the connection before calling again. See how others solved this on Reddit