Receiving an IPv6 address only proves local assignment. DNS, the default route and public reachability can still fail independently.
Test three layers
- Resolution: does the name return an AAAA record?
- Routing: can the device reach a known IPv6 endpoint?
- Application: is the browser waiting on a broken IPv6 attempt before falling back?
Change one variable at a time. Restore automatic DNS first, then compare IPv4-only, IPv6-only and dual-stack names.
Leave a useful record
Record the step that actually fixed it, the device or browser version, and any temporary changes you reverted. That note is often more useful than another bookmark.