The TP-Link MR6400 modem was bought and installed in November 2017 in our holiday house to give remote access to the smart house system (heating control, temperature monitoring, electrical power consumption monitoring). The configuration of the smart house system has not changes since 2020.

Since December 2019 the configuration of the modem has been the same with the same SIM card and the same ISP provider.

The TP-Link MR6400 has been running without any known problems since 2017 except for the last 5 months. During these 5 months the modem has failed to reconnect automatically to the Internet 3 times.

2025.08.29

No longer possible to connect remotely to the smart house system. I live 4 hour drive from the holiday house so a neighbor was sent over to the summer house to check. The status light on the smart house controller was blinking red indicating "No connection to the Internet" through the MR6400 modem. The power supply to the MR6400 was turned off/on, and the modem started up normally. Everything ok again.

2025.11.14

We were present at the holiday house and my iPhone lost connection to the Internet via the 4G connection. Apparently there were some problem with the data communication over the 4G network, and as expected the MR6400 also lost the connection to Internet. Within less that 60 minutes the iPhone was ok again and it was possible to browse the Internet over the 4G network.  BUT THE MR6400 DID NOT RECONNECT TO THE INTERNET. The MR6400 Wifi was ok but it was not possible to reach the Internet from Wifi and through the MR6400. The status lights on the MR6400 front was all ok except lights showing the 4G signal strength. THEY WERE ALL OFF SHOWING ZERO 4G SIGNAL STRENGTH.

Using my laptop I logged into the MR6400 web interface via Wifi. On the 3G/4G page the parameter ISP HAD THE VALUE "Not verified". (expected value is "Telenor") and the parameter Connection Status SHOWED THE VALUE "Not connected". (expected value is "Connected"). From the Web interface I did a Restart command of the MR6400 and the modem started up normally. Everything ok again.

2026.01.20

No longer possible to connect remotely to the smart house system. This time there was no neighbor to send in to check, and the weather forecast reported -30 degrees Celsius during the next days, Therefore I took the 4 hour drive to go and verify that the heating was ok and to check the MR6400. I arrived approx 16 hour after the problem with the Internet occurred. The status lights on the MR6400 front was all ok, also the lights showing the 4G signal strength had 4 dots turned on. I could connect to the Internet from my iPhone over the 4G network so the 4G network was ok on arrival. The Wifi network on the MR6400 was ok, and I could connect my laptop to the Wifi and connect to the smart house controller. BUT THERE WAS NO CONNECTION TO INTERNET VIA THE MR6400 MODEM. Using my laptop I tried to connect to the MR6400 Web page over Wifi, but my browser was not able to get to the Web page. I turned the power  supply of the MR6400 off/on and the modem started up normally. After that everything was Ok and it has now been working for 6 days without problems. It is important to notice that there is continuous traffic from the smart house system to the Internet via the MR6400 modem. The electrical power monitoring system sends the power consumption approx every 30 s to a cloud server.

Summary

TP-Link MR6400 failed to reconnect to the Internet 3 times during 5 months

Case 1: 1) No info about 4G network status before  the problem occurred 2) No Internet connection via MR6400 3) Power off/on fixed the problem

Case 2: 1) No Internet over 4G before the problem occurred 2) No Internet connection via MR6400 3) 4G network ok again within max 60 minutes but no Internet via MR6400 after that 5) 4G signal strength shown on MR6400 front is zero with the 4G network ok 6) ISP = "Not verified" and Connection Status = "Not Connected" on MR6400 Web interace 7)Running Restart command from Web interface fixed the problem

Case 3:  1) No info about 4G network status before  the problem occurred 2) 4G network ok when the fault analysis started 16 hrs after the problem occurred 3) All status lights on the MR6400 front is ok and 4G signal strength is 4 dots 4) No Internet connection via MR6400 5) Wifi network on MR6400 ok 6) Not possible to connect to MR6400 Web interface via Wifi 7) Power off/on fixed the problem

The questions are:

1. Should MR6400 be able to reconnect to Internet after a problem with Internet on the 4G network
2. Is the problem described in the cases above a known issue. And if yes can it be fixed by installing the newer firmware that is available for MR6400
3. Is it a problem if devices on the MR6400 Wifi continue to send data to the Internet if the MR6400 is no longer connect to the Internet

I see that I could have collected some more information when the problem happened. If it happens again I will

1. Try to ping the MR6400 from the 4G network
2. Log on the MR6400 Web interface and note all the parameters on the 3G/4G page
3. Upload the log from the MR6400
4. If not possible to connect to the MR6400 Web interface via Wifi I will try to connect vie the RJ45 ethernet port.