When that happen, look at the System\DMX Settings menu
If all 4 outputs are detected, this is more likely the issue described above, by @Matthias
If any is missing, that this is likely a hardware issue
Please also note, that when disconnected, the DMX PCB will auto recover Protection Mode, after few minutes, without the need to restart the console
What I did once, when I had this shortage issue, and only 2 DMX ports needed, is setting port 3+4 as 1+2. I would then switch the cables, from 1 to 3/ 2 to 4, back and forth, until the tech on stage found the problem.. In my case, it was a smoke machine spilling liquid, and causing that spikes over DMX lines...