I have a TL-MR6400 router with sim card entered. There is a problem when 4G Only mode is on. It seems that 4G upload is blocked by router somehow. Everything works fine with 3G Only mode on multiple devices. But when I switch 4G Only on problems appear. On my laptop everything is normal, doesn't matter if it is connected to router with cable or wirelessly, and the download/upload speeds are ok. But on my smartphone upload is 0 mbps and apps won't load it's content. Only a few internet pages will open via browser. But when I remove my sim card from router and put it in smartphone everything is ok, apps work and download/upload speeds are ok on 4G. I also noticed on my work desktop pc that some messaging apps won't upload a picture when connected to router with 4G mode on. So, when router shares 3G internet everithing is ok. But when it shares 4G internet upload is blocked and apps won't load on some devices. I assume there is a problem with concerned router because 4G internet of that sim card works fine when outside of the router. I also searched the internet and found many similar cases with 4G Only mode with concerned router. It works fine on 3G Only mode but when 4G Only mode is switched on then problems appear. People can't connect their phones, TVs, devices and so on. And there is no known solution so far. Few months ago I tried switching back between 4G and 3G modes and then 4G mode started to work normally when switched on from 3G mode. But that does not work anymore. So please, could you provide solution to this problem. How can we set 4G Only mode to work properly. I updated the firmware to the newest version for your information.