Join accept are shown but nothing happen

Hello Chirpstack community,

I just deployed my new Chirpstack infrastructure but i’m facing a strange issue.

I have several sensors of the same model, they were all connected to a previous network server (not Chirpstack) and i changed it to Chirpstack stack.

Once the migration was done i rebooted all the sensors, some of them were joining the network perfectly : Join request -> Join Accept -> Up (data)

But others are still not connecting. In the Lorawan frame reader i can see :
Join Request -> Join Accept -> Join Request -> Join Accept -> Join Request -> Join Accept -> …

Which means my gateway (Multitech Conduit IP67) is able to see the sensor and is validating the keys but it’s like the sensors are not receiving the join accept…

I’ve seen multiple topics about this kind of issue but i haven’t find any solution, can it be linked to the downlink frequency ? (if yes what should i configure for EU? and why some sensors are working?)

PS: to be more precise some sensors were directly working, one reboot and they connected, but some needed 2,3 or 4 reboot to join, they kept sending join request and they received the joined by chance one time (so maybe the frequency/ADR/SF was good this time?)

Thanks a lot it will be incredible if i can solve this :pleading_face:

[Update]

Ok, just tried to put a sensor closer to the antenna and it directly connected. What is strange is that the antenna was able to receive the join request before, so it’s not a coverage distance issue (?)

I think that the downlink join accept is not able to be received by the sensor when it’s far so it may be link with the SF/ADR or something… no idea

[Update[Update]]

Downlinks are working for 868100000 frequency but when my sensor is far it’s using 868300000 or 867300000. It seems that only 868100 is able to send downlink that’s why it can connect when it’s close to the antenna but other frequencies are not handling downlinks… how can i configure this ?