It sounds like the Tapo C520 is experiencing either a firmware-related bug or an issue with the motion detection/AI processing module, which has been reported by a few users after recent updates. When the camera works intermittently or misses events, the problem is usually tied to one of the following:

1. Firmware update not installing correctly

2. AI detection module crashing and failing to restart

3. Wi-Fi handshake instability during high activity

4. Corrupted configuration after multiple setting changes

Here are a few steps that commonly fix the issue:

Step 1: Reboot the camera from the Tapo app (do not just power cycle it)
Rebooting from the app forces a full software reload instead of only restarting the power.

Step 2: Reset the detection settings
Turn off motion detection, person detection, and AI detection. Save. Then turn them back on one at a time.

Step 3: Switch Wi-Fi band
If you are on 5 GHz, switch the C520 to 2.4 GHz. This model is much more stable on 2.4 GHz, especially with outdoor signal loss.

Step 4: Delete and re-add the camera
This clears any corrupted settings after a firmware update.

Step 5: Check the SD card
A failing SD card can cause recording and event detection to stop. Try removing it temporarily or formatting it inside the app.

If the problem continues after these steps, then it’s likely a firmware-side bug. In that case, your best option is to open a support ticket and include logs — TP-Link has been releasing incremental patches for the C420/C520 series recently.

I’ve also collected some troubleshooting notes and related device behavior patterns here:
inatbox