Some apps have their own auto-capitalization. Like Gmail or Twitter. This setting only controls Apple’s system keyboard. If you use a third-party keyboard (like SwiftKey or Grammarly), you’ll need to dig into their settings.
But for 95% of your typing? This fix is gold. You’ll thank me later. Or you’ll forget and blame the gremlin again. That’s okay too.
Just remember: if your phone ever starts capitalizing again after an update? Come back here. The steps haven’t changed. The gremlin just got a refresh.