@dobey Reformatting did the job. Thank you. Interestingly the name of the SD-card in the file manager is different from the one in the "External Drives " but works fine.

I have a similar problem on my FP2. When I start the phone, I am notified that a SIM card has been detected and I can see it in the "External Drives" as SS16G. However, I can not find it in the file manager as a media device or folder. It is listed in /dev/disk/by-id as mmsc-SS16G_0xf3c11129.
Any idea how to mount the SD card to be visible in the file manager ?

@grandpa

Why would UbPorts foundation with it's stated objective of respecting user privacy and open source software even remotely consider cooperating with the most intransparented IT-company in the world, bound to the regulations of an authoritarian anti-democratic regime ?
This would be the end of UbPorts foundation before it even has fully taken off.
This also nicely demonstrates the importance of being a foundation registered under German law because any activities in such direction could be in conflict with the foundation by-laws and objectives.

I tried to pair my Nexus 5 with my car's (Subaru Forester) audio system via Bluetooth. The phone detects the audio system but there is no dialog box to enter the PIN from the audio system in the Bluetooth setup. The audio system thus refuses the connection request. Is there any work-around for this ?
Thanks.