Hi everyone again,
i’ve got some new information. Just called the support today (yeah- spent about 1,50€ for a call to the netherlands). Esmée was very kind and told me that they are understaffed for the present situation (was to be expected) and told me- although I’ve already done most of these things- she first has to send me a standard-troubleshooting-mail as follows:
[…] I’m sorry to hear your proximity sensor is not behaving as expected.
Can you please try to make the move phone-to-ear to phone-away-from-ear several times when the screen stays black?
In extreme cases, removing the battery will shut down the phone and hence terminate the phone call. To avoid this you can preventively go to Settings > Accessibility > enable “Power button ends call”.
Because the proximity sensor is located on the upper left hand side of the device (on the left of the ear speaker), it may not be well behaving if you use a protective layer on the screen. (Please make sure you removed the plastic layer that was shipped with the phone.)
You mentioned you already tried to clean the screen and the inside.
If the issue is still occurring, I would like you to try a sensor-reading app (such as Sensors) and make sure the proximity sensor is working as expected. It should report either a presence (“0 cm”) or an absence (“5 cm”). The actual test is to cover and uncover the upper part of the device where the sensor is located.
If your proximity sensor is not reporting anything, or if its values does not change at all, please come back to us so we’ll start the takeback procedure. […]
This procedure with this standard-troubleshooting-mail may explain @blgreenaway 's half-hearted support answer.
Furthermore I’ve asked wether it is really necessary to actually bring in the whole phone instead of swapping just the misbehaving component.
In my (and maybe in the first couple of) case(s) it is neccesary, because they need example-phones to learn from and to investigate the failure of the sensor.
So my guess- whenever the support has cought up with the amount of pending issues, there will most probably be a simple exchange of the misbehaving module.
Which brings me to my conclusion- if this issue really bothers you- call the supprt and the phone will be replaced or repaired rather sooner than later. If you can wait a little longer- give the support some time to catch their breath and wait until your Email-request is being handled properly.
Last but not least, the support is so busy- they simply don’t have the time to browse this forum for new trouble or bugs. Call them if it is urgent and tell them what is happening (on your phone and in the forum) or write a message via the website if you can wait a bit.
Hope that’s some good news for all of us in here