Hello Twister,
You need to build depth maps at first and then use DepthMapsData as a source for the mesh reconstruction function the quality parameter should correspond for both functions and filtering option for the depth maps should be set to Mild:
chunk.buildDepthMaps(quality = PhotoScan.HighQuality, filter = PhotoScan.FilterMode.MildFiltering, reuse_depth = True)
chunk.buildModel(surface = PhotoScan.Arbitrary, source = PhotoScan.DepthMapsData, quality = PhotoScan.HighQuality, reuse_depth = True, keep_depth = True)