Yes, I have a SM-G950F
→ 2019-09-16 - 9-Pie - PDA: G950FXXU5DSHC - CSC: G950FTEN5DSH9 - MCP: G950FXXU5DSH3
In my estimation, your firmware is fine.
Now the question remains why some apps don’t work with the mobile network.Next, let’s check us the SIM status:
S8 > Settings < About Phone > SIM status > SIM status
A screenshot would be meaningful.
Tip: Anonymize your “Phone number on SIM” on the screenshot
This is an unedited screenshot, isn’t it?
What strikes me immediately is, that is written under
Phone number on SIM
Unknown
Your mobile phone number must be here!
Yes its unedited. Ordinary phone calls and SMS works just fine…
This is how it looks like with my S8 SM-G950F …
Which operating system does your host machine use: Linux or Wind°ws?
I use Windows, but also have access to Linux if necessary.
Do you want to leave it at the current status quo or do you want to continue searching for a better solution?
I need to figure out this problem or I have to flash another ROM 
Exactly. That’s what I would do.
Therefore I would do the following, namely update the BL_Bootlaoder and CP_Baseband firmware with Security Patch Level 2020-04-01 and then test again if the phone number is visible.
This can be done quickly and easily with Wind°ws Odin 3.14.4
OK thanks, I will give it a try!
If everything goes well on my S8 SM-G950F, then this should be possible on your device!
With the tool Samfirm v0-5-0 the download of the firmware is very fast in comparison to the snail’s pace with free download via Sammobile Approx.15 kB/Sec Non-Premium Members
Now I have tried to flash the firmware you mentrioned but with same result as before. I also tried to flash e Os once again. SIM Status is the same. The only thing that made my attention now was when I wiped the phone in TWRP it says “Failed to mount ‘/preload’ (Invalid argument)” Does that message sound like something goes wrong? I followed this guide when I installed e Os: [HOWTO] Install /e/ on a Samsung smartphone with Windows easily
Well, that’s not good to hear. I can only say that I’m basically already satisfied with the S8 and S8+ with /e/ OS 9-pie.
"In TWRP it says “Failed to mount ‘/preload’ (Invalid argument)” is a note I know of on various Samsung devices. I ignore it because it shows no effect.
/preload is a OEM-specific Partitions (Samsung), it’s used by stock ROM’s, holding some preloaded system apps and regional settings which are installed on first use.
The problem was the default APN, I changed some settings and now it works! 
While trying to flash /e/OS to my Samsung S8 (following the same HOWTO mentioned above), it ends up with “ERROR 7” and it says “Failed to mount ‘/preload’ (Invalid argument)”.
In TWRP there is also the option to wipe the preload partition. Would this probably help?
this is what the TWRP log says after the installation fails:
Hello,
try to use TWRP 3.3.1 instead of 3.4.0 (if it’s what you are using).
By the way, you could also use the Easy Installer.
For the staring issue (first post) you can try:
go to the APN settings
see if anything is set to IPv6
if so, change it to IPv4
Optionaly reboot
That may make a difference.
Hello
It didn’t work with the easy installer, i only came to the blue screen (i think it is called download mode or something like that).
But with ODIN and TWRP 3.3.1. it finally worked! 
Thanks for your support 