System Error on Edge 530

Today I have 2 System errors in the ERA Viewer that don't make much sense:

Error Name: System Error
Occurrences: 2
First Occurrence: 2022-06-09
Last Occurrence: 2022-06-09
Devices:
    Edge® 530: 9.10
App Versions: 1.0.2
Languages: cht
Backtrace:
    MyFitContributions.initialize:97
    MyField.initialize:32
    MyApp.getInitialView:140

The relevant code near MyFitContributions.initialize:97 is this:

        mSessionMaxHRField = dataField.createField(
            "xsh",
            4 /*MAX_HR_FIELD_ID*/,
            2 as Toybox.FitContributor.DataType,
            {
                :nativeNum => 17,
                :mesgType => 18 as Toybox.FitContributor.MessageType,
            }
        );

        mSessionMinHRField = dataField.createField( // this is line 97
            "nsh",
            6 /*MIN_HR_FIELD_ID*/,
            2 as Toybox.FitContributor.DataType,
            {
                :nativeNum => 64,
                :mesgType => 18 as Toybox.FitContributor.MessageType,
            }
        );

So I got the System Error on a line that is basically identical to the lines before it, the only difference is a few parameters (fieldId, :nativeNum). So it smells like a bug in edge530.
BTW: In simulator it works on edge530, and it works