Hi
Welcome to Apple Discussions
end up using my husband's PC which is HIGHLY annoying.
I would think it would be highly annoying to have a PC in the house. 😉
On a more serious note, Auto-fill depends on how the page/form is coded by the site developer. Some are very PC focused, which can create problems on a Mac.
Possible workaround: if you haven't done so, open Safari Preferences>Auto-fill. Select "edit" next to Other forms. There, remove the specific page not filling correctly. Close the panel.
Safari Menu>Empty Cache.
Now enter the URL(s) and complete the form again. See if that resolves the problem.