As you can see from the snapshot below the RAK811 is not able to latch/join to the LoRaWAN network using the “at+join” command, it’s after the 4th try that the RAK811 was able to join the network with “OK Join Success”.
Can you check your channels which are open and close using this command at+get_config=lora:channel?
When joining in EU868, channels 0,1 and 2 are the joining frequency so all must be off.
You can use this command to turn off other channels that are on at+set_config=lora:ch_mask:X:Y where X is the channel number and for Y it can be 1=on or 0=off.
Let say channel 3 is open and we need to close that, you will use the at+set_config=lora:ch_mask:3:0 command.
After turning off Channels 8,9,10,11,12 using commands that you mentioned
at+set_config=lora:ch_mask:8:0
at+set_config=lora:ch_mask:9:0
at+set_config=lora:ch_mask:10:0
at+set_config=lora:ch_mask:11:0
at+set_config=lora:ch_mask:12:0
I am now able to latch/join the LoRaWAN Stack v3 right away