Additive manufacturing processes such as the Laser Powder-Bed Fusion (LPBF) are associated with a large number of process parameters. Many of them can influence the microstructure or the porosity of the produced parts and consequently their high and very high cycle fatigue (VHCF) properties. In this context, process parameter optimization in regards to VHCF resistance requires accelerated fatigue testing methods such as ultrasonic fatigue testing. However, the defect and microstructure sensitivities of additively manufactured materials in accelerated 20 kHz fatigue response needs to be studied. This works aims to analyze this sensitivity and the effects of microstructure and porosity on the VHCF behavior of LPBF-Ti-6Al-4V. To do so ultrasonic fatigue testing is performed on five grades of LPBF-Ti6Al-4V that have different porosity levels or microstructures. These grades were generated using different LPBF process parameters and different thermal post-treatments. It was found that both material features highly influenced the VHCF properties of LPBF-Ti-6Al-4V revealing the sensitivity of accelerated 20 kHz fatigue tests to these features. Furthermore, both the size of porosity and the size of grains have a first order effect on fatigue strength. These sizes control the type of fatigue crack initiation. Moreover, an optimal temperature of thermal treatment for VHCF properties of LPBF-Ti-6Al-4V was found to be close to 920°C.