In this work, the increase on the filament conductivity during the 1st Reset operation, by using the incremental step pulse with verify algorithm, is investigated in HfO2-based 1T1R RRAM devices. A new approach is proposed in order to explain the increase of conductivity by highlighting the crucial roles played by both metal-oxide interfaces. The top metal-oxide interface (HfO2-x/TixO(y)) plays a role in the forming operation by creating a strong gradient of oxygen vacancies in the hafnium oxide layer. The bottom metal-oxide interface (TixOyNz/HfO2-x) also creates oxygen vacancies, which strengthen the conductive filament tip near to this interface at the beginning of the 1st Reset, leading to the reported conductivity increase. After the 1st Reset operation the conductive filament stabilizes at the bottom interface suppressing this behavior in the subsequent reset operations. By modifying the programming parameters and the temperature, it was confirmed a constant current increase of about 9 mu A during the 1st Reset regardless the operation conditions imposed.