The logs of the router do not indicate any issues.
The router itself maintains stable connectivity to mobile carrier throughout the whole running time.
Regarding wireless connections, I see a number of similar entries in the logs:
deauthenticated due to inactivity
<device_MAC> did not acknowledge authentication response
You could try doing the following modifications to the router's configuration, to see if it provides any improvement:
- Login to router's WebUI;
- Navigate to Network -> Wireless;
- Open access point interface settings;
- Switch to Advanced settings tab:
- Set slider button of Disable Inactivity Polling option to Enabled;
- Disable Disassociate On Low Acknowledgement option;
- Press Save & apply.
Also, could you name the specific device, which has once reported about an unstable connection?