Thank you Stokerg, it certainly has something to do with 32bit HDR because when I switch from Develop to Photo and the Raw RGBA/32 (HDR) file (which is dark) turns into RGBA/16 it becomes normally exposed, then if I return to Develop it still remains correctly exposed. The only problem is that if I want to increase the exposition pushing the cursor to the right my sky turns yellow and red ! (Nothing like that if the cursor goes left)
It must be something with HDR but in my Develop Assistant the RAW output format is RGB (16 bit) and Display Transform is well on ICC mode.
Anyway, thanks a lot for your help.