Autofill is the feature that makes a password manager feel invisible, so when it stops working the annoyance is out of proportion to the problem. Your saved data is ready the moment you sign in — whether through the desktop app or a Proton Pass login online — but filling still depends on three things agreeing with each other: the extension being awake and allowed to see the page, the page being willing to accept help, and the right saved item matching the form in front of you. Autofill failures are almost always one of those three layers breaking, and each has a different repair.
Check the extension before anything else
The most common reason autofill stops is that the browser extension is not running. Updates can disable an extension temporarily, a browser restart can leave it asleep, and a new browser profile starts with nothing installed. Confirm the extension is present and enabled, then reload the page you are testing on. If the extension icon is greyed out or missing, that single observation explains the whole failure and no further diagnosis is needed.
Permissions and protected pages
Even an active extension cannot fill a page it is not allowed to see. Browsers restrict extension access on certain sites for good reasons: banking portals, internal company tools, and browser settings pages are common examples. If autofill works everywhere except one specific site, permission is the likely cause rather than a fault in the saved data. Check the extension's site access settings and add the site explicitly if you trust it — but never loosen permissions for a page you do not recognise.
Two password managers is one too many
When two password managers run at once, they compete for the same fields. One fills the username, the other clears it, and the form submits with nothing in it. This conflict is easy to miss because both extensions appear to be working. Disable every other password manager or form filler while you test, then decide which one you actually want to keep. Two managers on one browser is not a backup strategy; it is a reliable way to break autofill.
Saved items that no longer match the form
A saved login is tied to a site's address and the way its form is built. When a site redesigns its login page, changes its domain, or adds an extra step, the saved item can stop matching even though the password is still correct. Open the saved item and compare its stored address with the page you are on. If the address has changed, update the saved entry rather than creating a duplicate. Duplicates are the second most common cause of "autofill does nothing" complaints, because the manager cannot decide which of three identical entries to use.
Forms that fight back
Some forms are deliberately difficult. Multi-step checkouts, fields that only appear after a delay, and pages that render inside frames can all defeat a manager that is working perfectly. The fix is rarely a setting. Wait for the page to finish loading before invoking autofill, use the extension's manual fill option to target the specific field, and save the item again once the form is fully visible. If a site consistently resists, save the credentials manually and accept that this one page needs a little more patience than the rest.
Clearing a stale cache
If autofill worked yesterday and does nothing today, a stale cache is a reasonable suspect. Sign out of the extension, clear the browser's site data for the page in question, and sign in again. This forces a fresh handshake between the extension and the page. It does not touch your vault; the data lives on Proton's servers and in your other signed-in clients, and a fresh sign-in simply pulls a clean copy.
When the problem is the site, not the manager
Not every autofill failure belongs to Proton Pass. Some sites block automatic filling on purpose, some use scripts that clear fields after they are filled, and some change their form structure every time the page loads. If autofill works on ten sites and fails on one, the manager is fine and the site is the variable. Report the behaviour to the site if it matters to you, and use manual copy-and-paste in the meantime. Recognising the difference between a broken manager and a hostile form saves hours of pointless troubleshooting.
Keeping autofill reliable over time
Two habits keep autofill working smoothly. First, keep the extension updated; outdated versions miss the page changes that updates exist to fix. Second, when a site redesigns its forms, revisit your saved items for that site within the first week. Fresh items fill; stale ones argue. A vault that is updated as life changes will autofill as reliably in five years as it did on the day you first installed it. For broader help with your account, return to the ProtonPass portal and review the sign-in guidance there.