Joining issues with smoke detector Zenner Easy Protect Radio

Dear Chirpstack Community,
I’m trying to add a Zenner Easy Protect Radio to my ChirpStack Server. According to the documentation, the expected byte order is MSB.

I use the Chirpstack Gateway Bridge to forward the packets to my Mikrotik wAP LR8 gateway, which is set to private. My network is operating in EU868.

The device is OTAA capable, and I have got the DevEUI and AppKey from the manufacturer. I also have got an APPEUI, but I assume this one is not needed for ChirpStack.

The device manufacturer says that the LoraWan MAC Version depends on the firmware version and can either be 1.0.1 or 1.0.2, but I cannot figure this out before connecting to the device. The manufacturer refers to the “Regional parameters EU868 with the certified stack 1.0.2”, so I’m not sure if this is A, B, RP002-1.0.1 or RP002-1.0.2.
I have tested the connection with both 1.0.1 A and 1.0.2 B; both don’t work:

After configuring everything in ChirpStack and waiting for the device to send the JoinRequest once every 24 hours, I successfully receive a JoinRequest, and the Application Server sends a JoinAccept in response and saves the activation data.
However, the JoinAccept does not seem do be received by the device. I cannot send any Downlink Messages, I didn’t receive the starting package it is supposed to send and every 24 hours, it issues another JoinRequest.

I have traced the path of the JoinAccept package, and it seems to be fine as in the traffic log of the Mikrotik Gateway it gets sent.

The only problem I could possibly conceive is that the Gateway seems to send the JoinAccept right away, without waiting the required 5 seconds.

I hope that you can help me to figure out this issue!

Best Regards

(Screenshots see below)

Device config with 1.0.1:

Device config with 1.0.2: (This is used in further screenshots)

Traffic on Application Server:

Traffic on Gateway: