Hello @Claus_Blem,
Thanks for confirming that the Kindle works as expected when using Windows.
We have seen a similar issue pop up before in this thread (Android app having trouble finding Linux Core) but unfortunately we have not been able to reproduce this in-house with any of our staff member’s setups or in a QA environment, even though we have collected quite a lot of information from affected customers and spent a considerable amount of time trying to reproduce in-house.
One way to verify if this is the same issue that you are experiencing is to perform this test:
• Open your Kindle Roon App and leave it open, having the QNAP as the Core
• Restart your QNAP
• See if you are able to connect after restarting
If you are able to reproduce this issue with those steps, some users have reported that they have been able to resolve this issue by turning off IGMP snooping on their Router.
I have found the manual for your router here and it does indeed appear to have the IGMP snooping option (page 139), although you will need to make this setting as a CONFIG command to the router (AT&T may be able to assist here with making that setting).
Please let me know if disabling IGMP Proxying improves the communication between your Android devices and helps resolve the issue with the Android devices connecting.
Thanks,
Noris