yes same issue on THREE UK network. Seems some people who reset default APN settings got it fixed but didnt work for me.
3G works fine
Only issue is 4G
I disabled VoLTE and this worked for me, but obviously I want to be able to use VoLTE!
Have spoken to Three and Samsung and both blame eachother
We all need to make them both aware of the issue so they provide a fix in next software update
Problem is likely to be with the Samsung update. I guess three will send the APN details again, but will fail once you switch between WiFi and data.
I can't believe something such as this was never tested.
The extra clicks to change the settings seems so primitive.
I've also started to experience this problem (I have the dual SIM variant but only use it with one SIM and an SD card). Like others, I've found that either disabling VoLTE Calls - or toggling Flight Mode on and off when switching between WiFi and 3G/4G - restores my cellular data connectivity.
However this is not a solution, the phone did not do this out of the box. I'm pretty hacked off that I have to disable VoLTE Calls which is a useful feature for me.
Enabling/disabling Wifi Calling makes no difference. However if I have VoLTE Calls enabled while connected to a wifi network, if I disconnect, immediately I have no cellular data. It magically starts working the moment I disable VoLTE Calls in the Settings -> Connections -> Mobile Networks menu.
My phone was given a full ADB diagnostic by the Samsung engineers at a local service centre last week and nothing untoward was indicated by the tests. This appears to be a new bug introduced by the most recent OTA update.