I’ve tried the solutions suggested in FAQ: Frequently Asked Questions for all DLS Courses, including restarting kernel, switching browser, and they do not help.
The submit assignment button disappears like a ghost 
I think it’s due to your subscription status. It’s says “upgrade to Pro” . You can’t submit without a subscription.
I agree, a Pro membership is required to have your assignment graded.
It might be the reason. However, I have payed for a one-month Pro Plan.
Even though, the platform kept asking me to upgrade.
There may be a problem with your subscription. Maybe it’s not been activated. The staff can support on this.
@community-team, can you look into this?
Hello,
I see you already have Pro Access.
Let me look into this and get back to you.
I will ask for your email via DM