If you have a Premium Plan, you should be able to add start date to your tasks. I’ve gone ahead and escalated this to our development team so we can investigate it further. In the meantime, could you please send me the URL of the task where you are not able to see the option? If you prefer you can send it to me via DM.
Is there any chance you could share a screencast with us? Our team is struggling to reproduce the issue and a screencat would really help us speed up our investigations! In your video screencast, we recommend that you use a Chrome Incognito window and have your Javascript console open:
Thanks for your follow up. After checking all the video setup and recording the video, finally, it is embarrassing to tell… I found out that those task without a start date is a “milestone”, which make sense… I forgot why in the first place I want to mark a start date on a milestone but… really appreciate your effort in checking this out and so sorry for the false reporting…