Zenfone 2 - ZE551KL - Dual SIM not working - how to make it work?

I have 2 AT&T SIMs, one for work, one for personal use.  I have a unlocked Zenfone 2 ZE551KL.  When I put in both SIMs, the phone knows that there are voicemails on both lines.  But then after a second or so, 1st line goes dead, there is an X on the antenna bars.  The Second SIM works fine.

I want to be able to make calls and receive calls on both lines.  Want to be able to Send and Receive Texts on both lines.  That only one line runs 4G data is fine.  ASUS reps told me this should work.  However, it does not, on line that has data set to 4G, I can make and receive calls, send and receive texts, but on the 1st line, business line, I can't make or receive calls, can't send or receive Texts.

What do the settings need to be so that it works on AT&T?

I have returned 2 phones to Amazon since it did not work.  Today I received a brand new phone from ASUS and still have the same problem.

Thanks for your help.

Frustrated ASUS Zenfone 2 user