Roaming problems in ap-sta (client) mode

Greetings,
I have a Nanobeam 5AC Gen2 which I run with the current OpenWRT version 23.05.3. The device is connected to a LANCOM L-822acn access point via Wifi using the 5 GHz module (ath10k). The Nanobeam is in client (WDS) mode as I bridge some VLANs between the AP and the LAN of the Nanobeam via this connection. So far everything works as desired.

However, I have problems roaming between several APs. All APs send out the same SSID. The Nanobeam also connects to the various APs without any problems if I force it to do so manually. But it does not do this automatically. If I connect the Nanobeam to an AP that has a signal of -70dBm and switch on another AP located directly next to the Nanobeam, it sees this AP with -40dBm according to the scan list, but it does not roam. It simply remains stubbornly in the last connected AP.

I have already tried the whole thing using 802.11r. The APs are configured for fast roaming. However, they indicate that the Nanobeam has not activated fast roaming. If I add "option ieee80211r '1'" to the wireless configuration file, the AP at least shows me that fast roaming is active. But the Nanobeam still does not want to roam.

What could be the reason for this? Is it actually intentional that no 802.11r can be activated via LuCI if the device is running in client mode?

EDIT: I use the ct firmware with ath10k ct driver and wpad-mbedtls (the full featured version)

Are all the APs configured on the same channel?