Yep, I was able to reproduce it on my test server. This is rare frontend bug that appears when custom quantity is enabled and initial quantity is set to 0.
In order to fix it, edit your product and set initial quantity to 1 instead of 0 or empty value. Then update your product and visit payment page again. Discounted price should be displayed fine now.
We will fix this issue so it won’t produce confusing results even when quantity is set to 0.
Thank you for reporting this and helping to figure out why this is happening.