T46G - BLF no work, Lamps wrong status

[ghostoll]

Hello,

We've been having a problem with all 13 T46G Yealink devices for a long time, when the internet download through the computer goes to maximum. Even after that, the device also shows malfunctions.
Due to the Internet load, the Yealink apparently loses the Internet connection at short notice and can not restore it to 100%. It shows malfunctions, such as the BLF buttons no longer work. The lamps show wrong status ....
Only a restart helps the device. Until the Internet shows full capacity again.

Firmware: 28.81.0.110

The phones hang on a switch. The switch directly to the "AVM Fritzbox 6490 Cable (kdg)".
Internet telephony is set up as a real-time application.

Internet test
Download 104159 kbps
Upload 11922 kbps
Ping 20 ms


Would anyone have an idea what it could be?

Regards