Hi Gerardo,
Its strange !!
Can you try creating the DSO in the BW again and reimport the Target BW Structure in DS. We have an option in Target BW which I dont remember. Can you please check and send me the screenshot.
Also did you restart the RFC Instance and check if the issue exists or not
Can you check if the RFC destination is pointing to a load balanced configuration. Also seek help from SAP BW Basis Team to understand if there are any recent configuration changes at the SAP BW side.
Regards
Arun Sasi