I reply to myself ....
After digging in files, I spotted folders in ressources/app/sia named host, renter, consensus ...
they contains databases for blockcjhain, hosts and renters info ...
The weird thing was that I've many versions of these folders located in the SIA-UI installation directory
AND in <username>/appData/roaming/SIA-UI ....
after different trials, the files in this folder might be the correct ones, as I have retrieved my SIA's storage folder and the UI shows 8 contracts , but the correct amount expected and storage used ....
INext time , I'll try the update feature in the App ...