@Pepe thanks!
@beaker Have a look here: Add heat sink or fan
The reason is in our case not the WLE1216v5-20, but the board-/CPU-temperature. (If you’d use the WLE900VX instead, the Wi-Fi is the one crashing earlier). Both will after some time exceed 100° C, which seems to be no problem for the WLE1216v5-20 (the industrial variant is explicitly stated to run under such conditions, but even the normal one has no outtakes), but the board will just crash at that point. I don’t remember if it’s exactly 100° C, but somewhat around that temperature - just run sensors to see the limit.