For your reference, there are some solutions as follows:
1. The video monitoring screen of the Xiaomi Smart Camera C300 has two modes: high-definition and automatic. The HD mode requires higher network traffic and bandwidth in comparison to auto mode. It is recommended to select automatic mode;
2. If you have selected automatic mode and still experience lag, it is due to poor Wi-Fi network conditions and heavy congestion.
You need to check the Wi-Fi routing, which can be done as follows:
1. The surrounding signal interference is serious, adjust the working channel and frequency band bandwidth of the Wi-Fi router;
2. There are too many Wi-Fi routing access devices, resulting in excessive router load and insufficient network bandwidth allocation;
3. The camera is far away from the Wi-Fi router, the signal is weak, and the network data transmission is unstable.