You had questions about the LM1 placement before the turbo. The boche spec sheet lists maximum operationg temps. I would assume this is why the LM1 has this warning.
Maximum temperatures (max. 250 h in 10 minutes intervals)
Exhaust gas at sensor element
- for standard sensor: <= 980°C
- for sensor with Inconel protection tube: <= 1030°C (8.3)
Note: If the exhaust gas temperature of 850°C
is exceeded, the heater power must be switched off