In current VVC design, there is an ambiguity in the derivation process for subblock merging candidate list. In detail, when ‘sps_affine_enabled_flag’ is set to 0 and ‘sps_sbtmvp_enabled_flag’ is set to 1, only subblock-based temporal motion vector prediction (SbTMVP) could be inserted into a subblock merge list. However, because SbTMVP is not always available, even if affine model based motion compensation is not used for inter prediction, a zero affine candidate is used as a subblock merging candidate. In order to prevent this ambiguity, this contribution proposes that SbTMVP candidate is always set available by setting to a default motion with zero reference index when collocated center subblock is not inter-coded. Simulation results reportedly show that Test 1 achieves 0.00% and 0.04% Y-BD rate changes for RA and LB configurations and Test 2 achieves 0.00% and 0.00% Y-BD rate changes for RA and LB configurations.