@VinitRaje 

Hi

We did the test and found that the device can also get an IPv6 address. Please provide the following information for further analysis:
1. SIM Carrier;
2. Have you tested the same SIM card in other routers?

  @Joseph-TP I'm not talking about 4G, which works as expected. The WAN of the MR600 is connected to my ISP's router's LAN. When I use another router in the same setup, the clients receive IPv6, but with the MR600, they don't. I believe the MR600 lacks an IPv6 passthrough or bridge mode.
 

I have exactly the same issue as described in this post, but it seems it still hasn't been fixed.

  @VinitRaje 

Hi

Thank you so much for taking the time to post the issue on the TP-Link community!

To better assist you, I've created a support ticket via your registered email address. The ticket ID is TKID240710410, please check your email box and ensure the support email is well received. 

Many thanks for your great cooperation and patience!