Problem between MIT App Inventor / HC05 / Arduino

Hi,

I have a problem when I would receive information from Mit --> arduino (arduino --> MIT is ok).
I use this block :
image

And with the arduino I receveived sometimes the good text "POM" and sometimes "PO�" or "POM" or "P�M".

An idea ?

Communication between arduino et HC05 9600 bauds.

Thanks
Best Regards