Users have the ability to temporarily disable it, albeit at their own inconvenience, by simply turning off "Show Lock Screen" within the Settings and Notifications option. The iOS 11 has been riddled with so many bugs and half-baked functionality that some of the users preferred to stick to the previous version.
Ask Siri to read your notifications and it'll read out all your recent notifications even if you hide the preview.
The site verified that the bug is in both iOS 11.2.6 and the beta of iOS 11.3. Siri bypassing the iPhone's lock and hidden notification setting is of major concern as users might have personal and confidential information on their WhatsApp, Gmail or even Slack.
The fix is likely to come in iOS 11.3, which remains in beta testing, but Apple might also address the problem in iOS 11.2.7. We tried again and again to get Siri to read texts, but it demanded we unlock our iPhones first. However it should be noted that this only seems to affect third-party apps and services, and that Apple's own apps like Messages do not appear to have been affected by the bug.
We've reached out to Apple and will update this story if we receive a response.
Test the bug for yourself: Go to Settings Notifications Select an app (say WhatsApp) Show Previews Select "When Unlocked".
It's likely that a fix will arrive in iOS 11.3, which is now in beta, although Apple could release a minor update to sort the issue like it did with the recent Telugu text bomb bug.