@Germanteam 

Hi, thanks for posting question on our community.

4G Internet speed can be affected by lots of factors, if you are experiencing low speed issue on TP-Link 4G LTE Router, please insert the same SIM card into another 4G device with the same UE Capability, such as LTE Cat4 or LTE-Advanced Cat6 etc., then compare the speed to see if it is really the router issue.

Once the issue is confirmed, please follow the steps below for troubleshooting:

Case 1: Both wired and wireless connections are slow on TP-Link 4G LTE Router:

    1) Go to Advanced -> Network -> Internet page and change Network Mode to "4G Only" especially when the router is working on 3G.

    2) Try another available APN profile or create a new APN profile manually.

    3) Try to select different 4G band(s) manually, refer to this  FAQ.

    4) Upgrade the firmware to latest version.

Case 2: Only wireless connection is slow on TP-Link 4G LTE Router:

    1) Change Wi-Fi channel and channel width on Advanced -> Wireless -> Wireless Settings page.

    2) Upgrade the firmware to latest version.