Are there any recent usability / UX and conversion studies how double entry of passwords while registration a user account in ecommerce shops slows down conversion rate? We try to ged rid of entering password twice. There is a "forgot password" flow anyways.
Double entry of Password is really unnecessary. To avoid mistakes, repetition during sign up is not a solution. Yes, there is "Power in repetition" but not in password confirmation. The solution is to provide the option to unmask the field associated with a strength indicator. Users make more errors when they can't see what they're typing while filling in a form. They, therefore, feel less confident. https://www.nngroup.com/articles/stop-password-masking/
When signing up for Facebook or MailChimp, you don’t need to enter your password twice
And it's true that user account in e-commerce shops slows down conversion rate. There is a famous case study by Formisimo where their newest version had only one password field for registration
You can also check this PDF
I don't think you need to refer to any studies/articles for this. The repetition during sign up is for avoiding mistakes during the password setup. A simple typo could lead to the user having to reset their password but
would the user actually know why the password is being shown to be wrong?
A typo, by nature, is mistake that gets overlooked. Which is why having to enter the password twice eliminates such mistakes. Also, "forgot password" is used to help the user when they "forget" the password. No one likes going through that flow, especially if they have just created their account.