First call goes to voice mail, 2nd answers

With my IPhone X and SPRINT, I find that when I travel to work, (Fremont, CA), the phone does not answer on the first try. I can even make an outgoing call first. First call, voicemail after 1 ring. Second call made immediately after will ring up to 15 times to prompt me to answer. The phone shows the missed call in the log. So got in the practice of calling myself from my work phone when I get into work in the morning so I don't miss my bosses call.. Well, today I did exactly that with exactly those results. Then didn't make or receive a call for ~ 3 hours. I then decided to call myself again... First call went straight to voicemail on the first ring, but the second call rang through "normally."

I've been on the phone with Sprint, they had me refresh, reload, restart, and anything else they can think of. My previous phone was a Motorola Pure X. Never had this problem. Also, I have coworkers who have an iPhone X on AT&T with no problems...

Does the IphoneX on CDMA use some battery saving protocol which results in missed first calls?

I'll rather have crappy battery life than miss calls.