@Sunshine >>> is your MR600 working as 3G/4G Router mode with SIM card inserted? Yes, off course >>> When the TL-R470T+ disconnected from MR600, please try connecting a client device to the MR600 via...

I tried first with DHCP and then static IP (out of the DHCP range), same result: After a certain time (? a few seconds to several hours) the TL-R470T+ is disconnected from the MR600. The devices use...