I experienced difficulties using the device tracker with a Fritz!Box (FRITZ!Box 7490) and a WLAN Repeater (FRITZ!Repeater 1200 AX):
Home Assistant (Device Tracker) showed a mobilefon as “abwesend” though it was connected to the WLAN via the WLAN-Repeater. I could not get the Device Tracker to work properly. Home Assistant showed the devices always “abwesend” (away) if they were connected to the WLAN-Repeater.
In [Home Network] → [mesh overwiev] there was no mesh-symbol at the WLAN-Repeater.
Solution:
Reconnect the WLAN-Repeater in a way that it is part of the WLAN-Mesh, as described here.
After reconnecting the WLAN-Repeater in the way described in the link above the Device Tacker worked as expected. Credit goes to this link.
I hope this information is useful to someone 