You are compeletly squared, should learn from your team members.
I did your test and this is what i get.. I CAN LOG IN using STOREFRONT.
https://www.loom.com/share/cbd0022fd55f479bbc35e67b2cc447d8
I understand you are upset, but i cant see anything that said that xstore its not the problem if you look my last video, your theme is using a special login form and changin login form my users can login. I think you are a very stubborn person.
Why did you insist giving us a terrible support? Give me another support agent and kick this case out of your hands. Please!!! I dont want you attend my case. I deserve a better agent than you.