I have nothing other than anecdotal evidence. But I have friends w XS-series phones, and I've seen moments on the same network where their phones don't work but others do. If you ever travel outside the city, I'd avoid the XS models based on what I've seen and read on these forums. For me personally, I'd take a refurb X, refurb 8+, or new XR instead.
All XS, XS Max and XR use Intel modems, Qualcomm hasn’t been available since the X, 8 and 8+... Next years iPhones will begin using Qualcomm again..I see! Could it be the issue with the different cellular modems causing the issue? Intel vs Qualcomm? I would like an XR though but it’s using a LCD.
If you want Xr, why not just get it? LCD is fine with your 7+. Xr will give you a modern all-screen design, and bigger screen than you have now, in a body size that is smaller. What’s not to like.