Installed it, worked fine. But a day after I installed, the option to import and export .psk and .psa files disappeared from the import menu and the export menu.
This is almost certainly a issue with your Blender configuration and nothing to do with the add-on.
Did you recently upgrade Blender? If so, did you make sure to re-install the add-on? Try toggling the enabled status of the add-on in your Blender preferences.
Unreal PSK/PSA (.psk/.psa)
Installed it, worked fine. But a day after I installed, the option to import and export .psk and .psa files disappeared from the import menu and the export menu.