FMI 3.0 reference FMUs log error messages even if loggingOn==fmi3False is given to the instantiate function:
Corresponding code fragment in cosimulation.c:

        comp->logEvents            = loggingOn;
        comp->logErrors            = true; // always log errors

However, the FMI 3.0 standard says:

If loggingOn = fmi3False, then any logging is disabled and the logMessage callback function
must not be called by the FMU.

I personally prefer that FMUs always report log messages when errors occur and would even prefer to weaken the sentence in the standard but we should deal with this inconsistency.