Hello @tristan_dragonheart 

Please give us more information. how did you measure By which.? 

• Perhaps the PC has a network card with only 100MBiT? 
• Is there a switch (Ethernet) in between that can only do up to 100? 
• Are there network sockets? Are all 8 wires connected there? If a wire is broken, you only have 100.For Ethernet (100) 4 wires are enough.Gigabit, all 8 wires are required. 
• How does the Fritzbox synchronize? It's on the overview page when you log in. Attached to ... 
• Can you measure with the smartphone with 5GHz in the WLAN, next to the Fritzbox? Do you have over 100? 
• Please answer all questions accurately. It sounds like you have an ethernet connection on the internal network.