Webmail randomly prompts for password

Occasionally, I'll write an e-mail using webmail (win 10/chrome) and when I press send, the e-mail disappears and a window opens prompting for a password.  The only problem is that my password doesn't work and I lose my e-mail.

 

Any Idea how to turn this "feature" off.  It's cost me hours of wasted time recreating e-mails because there's no way to go back and since it doesn't like my password, it tells me to try again in some random number of hours and minutes.