I'm having the same issues as everyone else . I have the Samsung 4G LTE Network Extender 2 (SLS-BU10B). I started using it in June and it has worked flawlessly until today. I got the MME Communication Failure this morning and have tried every tip posted here. When I reset it, it will work for between 2 and 20 minutes and then I get the same error. I discontinued my landline and count on this device for my home phone service so I'm not very happy at this point. I doesn't look like there are any right answers here.
Had to re-start it once or twice a day. What worked for me is going into my router configuration. I went into the DMZ section and added the network extender IP address under IPv4 .Two days now and no interruptions