MATLAB: Problems with BytesAvailableFcn in App designer

app designerbytesavailablefcn

I write in this forum to see if someone could help me solve the problem I have with the BytesAvailableFn function. I am developing an interface using the matlab app designer but when I run the code the program does not access the read function (I have put a debug to check it) and I do not understand where the error may be. The problem is that this code works in Guide but in App designer it does not. Thank you very much I hope for your help. I enclose a fragment of the code:
            app.t_waveforms.BytesAvailableFcnMode = 'byte';
            app.t_waveforms.BytesAvailableFcnCount = app.buffer + 8;
            set (app.t_waveforms.BytesAvailableFcn, @read);
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