When I try to log into my brokerage account and allow Safari 10 to autofill the password, it consistently enters the wrong password. Safari > Preferences > Passwords has the correct one but I always have to type it in manually rather than use autofill.

I have deleted that site and password info from the preference pane and re-entered it manually (Safari asks if I want to always allow, and I agree) but the next time that I try to log in, the same thing happens. I have also cleared Safari caches, to no effect. This does not happen with any other website. This behavior is not new with Safari 10; it happened in Safari 9 as well.

How can I make Safari autofill the correct password?

macOS 10.15.6, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365