NR5101 4G doesn't work with external antenna

I just received a Zyxel Nebula NR5101 that I bought to change out my 4G router. I have the 4G router connected to a 5G antenna and get about 45mbit down and 15mbit up. I connected this new router and now get 10mbit down and 2 up. A serious disappointment. I quickly realized that the router only uses the internal antenna for 4G and not the external antenna. I've now read that this is actually how this router functions. Can this be true? For this extremely expensive router and not even the function of 4G to the external ports? Is there really no way to disable the internal antenna and use all the frequencies of the external antenna? Any update that fixes this available?