I'm not confident that any thing below is going to help, but there's a few things which are worth knowing which may at least save some time.
The lock / unlock / keyless start all use bluetooth but not the pairing kind of bluetooth used for calls etc (Bluetooth LE ?). I've unpaired my phone from the car completely and keyless start etc still work. It's probably worth doing this while testing stuff.
The lock/unlock on the main screen used to only do network lock/unlock, and the lock/unlock in the remote key management did bluetooth lock/unlock. At some point they changed this so that the controls on the main screen try bluetooth first which is immediate, but if not available then network control which can take up to 30 seconds and sometimes fails.
Having activated the bluetooth key once which requires the network, you can turn the network off (mobile and wifi) just in case there is some kind of interaction.
You get different messages from
@Martinonline and me. E.g. on keyless start we get the 120 seconds message. This seems to be dependant on whether you use the main screen or the keyless management screen. These days I only use the main screen.
If you want to recalibrate the keyless entry, it seems the only way is to uninstall the app and reinstall (Or from android settings for the app, stop the app and clear all data which is effectively the same). I suspect you've already cleared all data, but It may be worth trying this anyway.
Unlocking the car, opening the door and pressing keyless start before sitting down gives the success message and 120 second info. Thereafter I can sit down, press the brake and drive away with no further messages on the phone or car.
If I sit down before pressing start I get the key not detected message. Presing start still shows the key not detected message (a bug I think), but lifting off of the seat and sitting back down again turns on the car as normal, and you can drive away as normal. Instead of sitting down a 2nd time I think you can just press the brake pedal to go straight to Ready mode.
The phones I have used are all Samsung A series A20, A40, A51, A14, not the most up to date especially with regards to the bluetooth version. It may be worth trying one of your other phones with an older version of Bluetooth on.
As mentioned above, as it doesn't use pairing your previous bluetooth updates may not have affected bluetooth lock/start operation etc.
Note, while buggering around with the above I've had a few odd bits of behavior such as setting the alarm off (went straight indoors for the real key) and also a battery warning (probably pressing the brake before the car's fully on). I'm always worried I'll end up locked in and the alarm going off but it's not happened yet.