Mmm, this is interesting ...
... the problems I reported in this forum few days ago are for a Jaguar XF ...
Anyway, an update on the problem.
The problem is definitively random: yesterday everything was working smoothly: no more random disconnections from the car system, all phone and streaming service available and perfectly working (without any intervention from my side). This morning the problems are back again, without any change to the phone or car settings.
few days ago I've upgraded S8 to android 9 (official upgrade) and I have same exact problems, so problems are not only with s9 but also with s8. I have similar problems, bluetooth keeps connecting and few seconds later disconnects and it repeats. It happens also that I have Land Rover Disco Sport - so for sure it have same software/firmware as your Jaguar as this is smae manufacturer.
I've read whole thread, tested all options and it worked randomly as you said... it stopped working today again but i thought about all options people were posting here and many of them are connected to battery optimizations, and your "randomness" problem has sparked also some thought in my head. My conclusion is that Phone is killing BT connection because it want to optimize battery live to aggresively and i found workaround for this - you need to plugin phone charger. Once it is connected it to power source it does not want to optimize battery life so aggresive and BT connection works normaly - this is only workaround and it should be fixed by Samsung but it shows that this is just a bug in software. Randomness in working in my case was caused by that not always i connect my phone to charger
and i found workaround for this - you need to plugin phone charger.
Have to edit this reply, March 22:
This works temporarily fine with my S9 in my Jag XF (X260).
I have tried the energy settings / battery optimization before, that did not work. But this time with the cable plugged in it was absolutely fine. No idea if it made a difference that the phone was nearly fully charged. I also had an original USB-C cable spare.
Of course this cannot be the final solution, even though I am already thinking to buy one of these wireless cupholder chargers, as I put the phone in the cupholder anyway, but until they fix it is a good way to deal with it...
Edit: It seems that I need to plugin phone charger a few moments before I start the car/infotainment; otherwise it happens quite often that the bluetooth connection is interrupted immediately... in these cases the phone does not ask all the "allow access" questions, especially the final one, contacts, is not reached, since it drops out before...
But I am not 100% sure, because I just stopped messing around with that cheesy S9...
I thought you'd found the solution however it seems not .. My tests as follows
1. Complete factory reset with only stock apps installed no charger - lost connection
2. Complete factory reset with only stock apps installed in car charger - lost connection
3. Complete factory reset with only stock apps installed. Extension lead from house with fully charged battery and plugged into a fast charger and all fingers crossed - lost connection
So it seems at least for the Land Rover Discovery Sport the issue remains with n=1
Any other ideas please send them over. My phone is going back again today by post so hopefully Samsung will find the problem second time around. They have much more detail now so hoping for a positve resolution
KH20, did you also charge with the original Samsung USB to USB-C cable, directly from a USB port, or with the cigar lighter thing? (I did it with the USB port and original Samsung cable...)
Yes I used the original charging cable that came with the phone, I also have a BMW 4 series and aftermarket cables do interfere with the Idrive system so always use genuine Samsung products to avoid problems.
There are a few charging points in the Land Rover Discovery Sport and i plugged into 2 of them. I also used the Samsung mains charger on an extension lead to see if that works but no sucess.