To workaround this issue, you can run XPSExplorer.
The CA.SM::$AgentDiscoveryEnabled object can be modified through the XPSExplorer tool with the following steps:
1) Login to Policy Server, and open a CLI.
2) Go to /bin folder under your Policy Server install path, and run the XPSExplorer tool.
3) On the main menu, type F and hit enter, in order to do an object search (as this is a parameter which we cannot browse).
4) When asking for the XID/RID to be found, type:
and hit enter.
5) The object will be displayed and you would see the current parameters. Type W and hit enter to modify the object.
6) Type the number 1 for DefaultValue field and hit enter.
7) Type 0 and hit enter, as we will set this new value.
8) Type U and hit enter, to verify the value is set to 0.
9) Type Q and hit enter to return to the main menu, and type P to sync the changes with the Policy Server.
10) Type Q and hit enter again to exit the tool. Now, launch the XPSSweeper tool to ensure the data is synced.