Sigma has released firmware Ver.02 for their 100-400mm F5-6.3 DG DN OS | Contemporary lens for Sony E-mount.
The firmware addresses the two following issues:
・It has improved the phenomenon whereby the lens’s optical stabilizer effect differs depending on the shutter type and drive mode used.
・It has corrected the phenomenon whereby the lens firmware cannot be updated via the camera.
Unfortunately it seems that the firmware cannot be updated from Ver.01 to Ver.02 by the end-user via the camera. Therefore, Sigma will update the lens firmware free of charge. Of course, this unfortunately means that you will nee to send the lens off to them, and will most likely incur a hefty shipping charge when you add the shipping insurance.
I find it quite bizarre that in 2021 a lens needs to be returned to the manufacturer to update the firmware, and I suspect that many existing owners will not want to go to the trouble.