I have been using a Fylesystem Write file for months which works very well, including in simulation. However, the file is no longer written and does not generate an error after a build in version 4.9.72.
I redid the build in 4.7.37 and it works again.
In fact in 4.9.72 it seems to me that the system request to assign the right to write during the first use is not triggered. It appears from the first save in 4.7.37.
Thanks in advance.