R6700AX WiFi 2.4 Connection Issue

Firmware V1.0.10.110

Wireless Settings:

- Enable AX: checked

2.4G:

- Enable SSID Broadcast: checked

- Channel: Auto

- Mode: Up to 600 Mbps

- Security: WPA2-Personal

5G:

- Enable SSID Broadcast: checked

- Channel: 153

- Mode: Up to 1200 Mbps

- Security Options: WPA2-Personal

Advanced Wireless Settings:

- Enable Wireless Router Radio: checked

- CTS/RTS Threshold: 2347

- Preamble Mode: Automatic

- Transmit Power Control: 100%

- Turn off wireless signal by schedule: unchecked

- Enable MU-MIMO: checked

- Disable PMF: unchecked

It took me a while to come back on this because I tried the 2.4G connection via different devices. It turns out that after I shut down my printer for a while, none of my devices, including my iPhone, my iPad and my laptop, can connect to the 2.4G network. So it doesn't seem like an issue particularly to my printer.

Because my printer is the only device that connects to 2.4G, while all the others are connected to 5G . Once it's shut down, the 2.4G is unused. It feels to me that the 2.4G would turn into some sort of sleep mode after a while. Now I force my iPhone to connect to the 2.4G so that there's always a live connection. Now the issue is gone. My printer can always connect when it's turned on.

Is it true that there's a sleep mode? If yes, is there a way to disable it or any other solution please?