UWP: Insufficient memory on release build

UWP app with RichEditBox has memory and other type issues on release configuration with code optimization enabled. On debug or relase with non optimized code it runs ok. Following code is inside a method running on the thread pool (await Task.Run(() => MyMethod(richEditTextDocument));

    // Getting text for first time works
    richEditTextDocument.GetText(Windows.UI.Text.TextGetOptions.None, out string rtbOriginalText);

    foreach (Match v in wordMatches)
    {
        try
        {
                // In release mode with optimized code, 
//at very first iteration, line below throws 
//"Insufficient memory to continue execution of the program"                        
                Windows.UI.Text.ITextRange selectedTextNew = richEditTextDocument.GetRange(v.Index, v.Index + v.Length);

        }
        catch
        {
            continue; //insufficient memory
        }

    }


    // In release with optimized code, calling GetText for second time throws
    //(Exception from HRESULT: 0x8000FFFF)
    //   at System.Runtime.InteropServices.McgMarshal.ThrowOnExternalCallFailed(Int32, RuntimeTypeHandle) + 0x21
    //   at __Interop.ComCallHelpers.Call(__ComObject, RuntimeTypeHandle, Int32, TextGetOptions, Void *) + 0xc2
    //   at __Interop.ForwardComStubs.Stub_67[TThis](__ComObject, TextGetOptions, String &, Int32) + 0x44
    //   at Windows.UI.Text.RichEditTextDocument.GetText(TextGetOptions, String &) + 0x23

    // Thinking that it can be fixed setting selection to 0 before GetText, but...
    richEditTextDocument.Selection.StartPosition = 0; //, this line throws insufficient memory
    richEditTextDocument.Selection.EndPosition = 0;

    // HRESULT: 0x8000FFFF (if execution reachs here, deleting two previous lines)
    richEditTextDocument.GetText(Windows.UI.Text.TextGetOptions.None, out string rtbOriginalTextAnother);

Submission to store was rejected two times because of other minor errors that went fixed, but at third time it passed the test and was published, whithout noticing this error, that is part of the main function of the app and lets it "unusable" (as they (Microsoft) said the other times). Submitting a non optimized code building (but with NET native toolchain) complains about missing DEBUG dlls. I noticed the error but, as disabling code optimization when debugging the release "fixed" it (as is explained at https://devblogs.microsoft.com/devops/debugging-net-native-windows-universal-apps/ linked by official Microsoft docs at https://docs.microsoft.com/en-us/windows/msix/package/packaging-uwp-apps), i forgot that it only was being "ignored". So, first time publishing and got an unusable app.

App uses nuget packages NewtonSoft.Json, Win2D.uwp, Microsoft.NETCore.UniversalWindowsPlatform and a "normal" reference to Microsoft.Advertising.Xaml (also app is not showing ads in production, ErrorOcurred gives NoAdAvailable)

Thanks