The Hardware Stuff First

When I opened it up, I found the internal data cable was slightly pressing against the deadbolt. Nothing crazy, but enough that it was straining a bit. I gently tucked it away and that helped with responsiveness. Some people in the Aqara forums actually chiseled a tiny channel inside the door pocket to give the cable more room — didn't need to go that far, but worth knowing if you're desperate.

Also verify the tailpiece is centered. Open your battery cover, remove the battery, manually turn the knob. If it's grinding or sticking, the tailpiece might be off-center in the deadbolt hole. Loosening the mounting plate screws and adjusting its position fixed that for me.

And make sure the deadbolt isn't rubbing against your door's strike plate. Obvious but it happens.

The Calibration Loop

If your Aqara Home app keeps saying "Unknown" status and asking you to recalibrate constantly:

Easy way: Open Aqara Home app > Settings > Door Lock Calibration > close the door (keep it unlocked) > tap Start. Let it map the orientation.

Offline way (if your WiFi is being weird): Remove battery cover, press Set button once, press 5 on the keypad, follow the voice prompts. This actually worked better for me than the app method.

The Big One: "No Response" in HomeKit

This is what was killing me. The lock works fine in the Aqara app but HomeKit just spins forever.

The fix that actually worked: I completely unaired the lock and re-added it in a specific order.

1. Remove it from HomeKit entirely
2. Scan the Matter QR code directly in the Apple Home app FIRST (let it join Thread natively)
3. Wait like 5-10 minutes for it to stabilize
4. THEN go back and add it as a secondary bridge through the Aqara app (generate a new pairing code in HomeKit settings, copy it to Aqara Home, bridge to Hub M3)

Sounds complicated but the order matters. HomeKit direct first, Aqara app second. That sequence fixed it for me.

Also — and this might sound weird — I disabled my 5GHz WiFi band temporarily during setup. Just 2.4GHz + the Thread network. Once it was stable, I turned 5GHz back on. I have a UniFi network and apparently that was interfering.

Keep the lock within like 3-5 meters of your Thread Border Router or Hub M3. Weak mesh signals cause constant dropping.

UWB Unlock on Approach Not Working?

Don't use HomeKit's auto-lock toggle. Turn that OFF and instead use the Aqara Home app's auto-lock feature. HomeKit's timer apparently doesn't know when the door is still open, so it'll lock while you're approaching. The Aqara app version is better.

Also make sure "Unlock on Approach" is toggled ON in your Apple Wallet for the digital key. Sounds obvious but I forgot to check.

Nuclear Option: Hard Reset

If the firmware is completely stuck:

1. Remove the rear battery cover
2. Press and hold the Reset key for 5 seconds
3. Verify your admin password when it asks on the keypad
4. Lock clears everything

Used this once when the firmware locked up. Worked.

Quick Note: Aqara U50

If you're looking at the Aqara U50 (the Zigbee variant), just be aware some U50 models are hybrid Zigbee + Matter. Double-check yours actually supports native Matter/Thread in HomeKit or you might need a hub bridge. The U400 doesn't have this problem — it's just Matter/Thread.

Anyway that's what worked for me. Is anyone else dealing with this? Curious what fixed it for you guys or if you found other solutions I'm missing.

Sources:
https://store-support.aqara.com/products/smart-lock-u400
https://eu.manuals.plus/aqara/u400-uwb-smart-lock-manual