ok, since it doesn´t even try to launch retroarch it seems it is something related with ES and core name or path.... I can be that ES wants to launch standalone PPSSPP emulator instead libretro core...
you can try this little hack, rename your psp core filename to psp_libretro.so then edit your es_systems.cfg file and change back the 144 line
to
<command>/storage/.kodi/addons/game.retroarch/addon.start psp %ROM% ES</command>
Also you can go back to ppsspp line in es_systems and try using PPSSPP standalone emulator, by the way PPSSPP standalone used to had better performance
Mario77 do you launch PSP libretro core from ES and it works ok for you?
* please attacth all log files everytime because I need to follow the trail... XD