Login name and password not filling in for one particular website.

Hi there Curtis,

If I understand correctly you aren't seeing the option to automatically fill in your username on a particular website where it used to show before. I would start by quitting the Safari app first:

Force an app to close in iOS

1. Press the Home button two times quickly. You'll see small previews of your recently used apps.
2. Swipe left to find the app you want to close.
3. Swipe up on the app's preview to close it.

When you have done that restart the device and test the issue again:

iOS: Turning off and on (restarting) and resetting

If AutoFill still is not showing check to make sure it is still enabled:

Go to Settings > Safari > AutoFill, then turn on Use Contact Info. Then, tap AutoFill above the onscreen keyboard when you’re filling in the form. Not all websites support AutoFill.

From: Fill in forms - iPhone

Take note of the bolded underlined part. It is possible that there was an update to the site that removed support for Autofill. Another thing you can do is delete all website data from the phone and to see if cookies are enabled as well. That could potentially bring the function back:

Safari web settings on your iPhone, iPad, and iPod touch

Thank you for using Apple Support Communities.

Hey there, thanks for the update. Next I would recommend that you backup your device to iTunes, then restore it as new and verify that it works.

How to erase your iOS device and then set it up as a new device or restore it from backups
If it does, then restore your backup to either verify it still works and the software just needed reinstalled, or isolate the issue to the backup file itself.