iPhone 15 Pro on iOS 18.6+ Loses Data Connection When Switching Between Wi-Fi and Cellular

Bug Report:

Device: iPhone 15 Pro

iOS Version: 18.6 (and all subsequent updates) (no issues before these updates)

Issue:

Whenever my phone switches between Wi-Fi and cellular data (and vice versa), I lose internet access entirely. The phone shows it is connected to the network and even connects to Apple CarPlay, but there is no usable data connection.

Frequency:

This happens multiple times per day. I often need to restart my iPhone up to 8 times in one day.

Expected Behavior:

The phone should seamlessly switch between Wi-Fi and cellular data without losing internet connectivity.

Actual Behavior:

The iPhone loses all data connectivity when switching networks, requiring a full restart to restore internet access.

Impact:

This significantly disrupts daily use, including CarPlay navigation, messaging, and general connectivity.