Hi all,
The issue is solved. After poking around and trying different things without success (including the attempt of a reinstallation with the ubports installer - no device found or several communication errors) I just did a full reset of the device as a last option.
Success! Unfortunately I had to wait until I had the opportunity to test the LTE function in an area with good LTE coverage - therefore the delay.
But now everything is fine. The phone connects automatically to the network, no manual input of APN data is necessary.
Sometimes solutions are too close to see them.
The root cause of the problem, however, remains unknown.
Thanks again for your support and tips
Mat

@Fla
Addendum: I just checked the interfaces and got:
ccmni1 Link encap:Point-to-Point Protocol
inet addr:10.24.58.241 Mask:255.255.255.0

rndis0 Link encap:Ethernet HWaddr a6:72:65:18:f2:93
inet addr:10.15.19.82 Bcast:10.15.19.255 Mask:255.255.255.0

However, pinging an official IP-address doesn't succeed, probably the above IP-address (ccmni1) is not assigned by the provider.

@fla
I got the error message
Error setting context /ril_0/context1 property Protocol: org.ofono.Error.InUse: The resource is currently in use

"L" is shown in the status bar, so the context should refer to lte?

@fp2andfp3-user
Thanks a lot!
Do you use UT with an Congstar LTE plan or just 3G?

@Keneda
I think I could, give me a free day to focus on that

@stanwood
Yes, I'm on stable. Good idea! I'll try this the next days and report.

@Keneda
Unfortunately I just have no Vollaphone with Android to test it.

Thanks a million
Mat

@kristatos
Thanks to all for your tips.
My carrier is Deutsche Telekom (Germany). With an Android mobile all works pretty well. It's a nano SIM (about 1 year old, should meet the requirements, up to 300 MBit/s are supported).
And yes, I tested it in several locations with very good reception conditions. No success.
If 3G works, 4G not, are there any special/expert APN settings affecting 4G? Maybe to be configured via CLI?

@stanwood
yes, I did. By toggling between 2G/3G and 2G/3G/4G I could verify that the problem is on the LTE-side. 3G works as expected. Returning to LTE, the error occurs.

Hi all,
I'm new to UBports, using a Vollaphone. The UBport-developers did a great job supporting this nice mobile!
I noticed that all basic functions are working fine, LTE however fails. With 3G I can connect to the internet. Using LTE I get a Name Resolution Error. I searched the forum without success. Sorry, if I might have overlooked something.
Is this a known problem? If not, what can I do to collect more debug info?
Thanks a million for your hints and help!
Best,
Mat