Yes i can see a return value 3 in the MSI install log:
Action ended 08:08:31: InstallFinalize. Return value 3.
Action ended 08:08:31: INSTALL. Return value 3.
I have not used PSADT itself to manage restarts of the computer but since FortiClient installs a kernel module and windows have to restart to complete removal of that module. Once “clean” it can install the new module.