In The Netherlands (with T-Mobile) we do have this problem too for almost a year. The iPhone X, 8 and 8 Plus have problems like:
- No 4G;
- Dropped calls;
- Slow speeds;
- More often 'no service'.
You can read them here (in Dutch):
https://community.t-mobile.nl/apple-444/slechte-verbinding-met-iphone-283693
This occurs to a small percentage of the users, but is really annoying. The worst part is that neither T-Mobile or Apple came up with a solution, apart from swapping the phone for a new or refurbished item. This is still going on.
I have bought an iPhone XS Max and I'm using it for almost 3 days. I cannot really determine if the reception is worse than my iPhone 7 Plus. The speeds are better than my 7 Plus. The only thing that I have noticed is that this iPhone loses the 4G connection a little bit faster than my iPhone 7 Plus. Moreover, when I place the iPhone XS Max in my pockets, it drops easily to 3G where the coverage is less. I hoped it would perform better, since it has 4x4 MiMo. Overall, the speeds are pretty good since we have 256-QAM for download and 64-QAM for upload and triple carrier aggegration across the country. Here are some examples:
At home, I have around 180 Mbits download and 45 Mbits upload.
The iPhone XS Max uses the same frequencies like my iPhone 7 Plus had. You can view the configuration here:
I'm not sure if the reception is worse than my old 7 Plus. I went for a 70 km (44 miles) ride with public transport ride today, which I do 200 times a year, and the patterns were almost the same. Sometimes it held the 4G connection longer than the 7 Plus, sometimes it didn't. The strangest part what I had noticed, was that I achieved around 17 Mbits of download speed over 4G (one bar) and the connection dropped to 3G. I made a GIF from that.
I'm hoping that these devices won't have the same problem as the iPhone X, 8(+) have with T-Mobile Netherlands.
Fingers crossed.