I believe that my local cell/tower switches itself into low power mode at night, as an energy saving method. 

My router loses the 4g connection at the same time every night at about 11.30pm and automatically switches to 3g. The following morning I will see that it is still in 3g and I have to manually switch it back to 4g. 

I have tried setting the router to automatically reboot itself at 6am for example, in the hopes that it will auto connect to 4g but with no luck, as it just connects to 3g. 

Is there something I am missing? Is there a setting I can change to resolve this?

My phone's SIM is on the same mobile network / operator and I can it also loses the 4g at night and regains it back in the morning, but with no problems and is automatic. 

I believe this issue is with just this particular router.