iPhone 11 repeatedly dropping connection to cellular

It seems iOS18 might have broken something for cellular connections. Ever since its update, the iPhone 11 is dropping cellular connections randomly. iPhone is currently on latest iOS 18.2. What the issue looks like:

Cellular network shows as a few bars, working perfectly fine. Then, suddenly, the cellular connection disappears, sometimes zero bars, sometimes the SOS signal. This happens while on wifi and while not on wifi. It sometimes automatically comes back, sometimes I need to manually select airplane mode and turn off again to restore the cellular connection.

• I've tried all the local settings, including resetting the network settings.
• I also put another iPhone on the same network, to compare, but iPhone 2 (16 pro) has no issues whatsoever.
• I've tried moving away from physical sim to esim, to no avail.
• Automatic network selection toward manual selected network did not solve the issue either.
• I've installed different esims in different countries, with still the same issue.
• Furthermore, I have tried all the suggestions online, like turning on and off roaming, restarting the iPhone, etc, without a solution.