GAH is AOL's sign in system and a 1111 with correct credentials on one device while another works is the signature of that specific device or browser's state rather than the account, since the account clearly signs in elsewhere. The fixes:

The browser state, most common for web sign in: stale cookies and cached sign in scripts for AOL on the failing device corrupt the flow. Clear cookies and cache for the AOL domains, or test in a private window, the private window working confirming it and pointing at a targeted clear followed by a fresh sign in.

The extensions and security software, second: ad blockers, privacy extensions and overly aggressive security suites interfere with AOL's sign in scripts on one browser while another browser or device without them works. Test with extensions disabled or a different browser, then allowlist AOL where the offender is found.

The stored credential mismatch, for a client rather than web: a mail client on the failing device holding an old password or a normal password where AOL now needs an app password fails to sign in while a correctly configured device works. Regenerate an app password and update the client, the app password being AOL's requirement that catches devices set up before two step verification was enabled.

The time and date, the surprising one: a device whose clock is significantly wrong fails modern sign ins, since the security handshake depends on accurate time and one device with a drifted clock failing while a correct one works fits your symptom exactly. Check the failing device's date, time and timezone are correct and automatically set, a two minute check that resolves a surprising share of one device only sign in failures.